Patent Publication Number: US-2010110246-A1

Title: Image sensor and method of manufacturing the same

Description:
PRIORITY STATEMENT 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2008-0108385, in the Korean Intellectual Property Office (KIPO) filed on Nov. 3, 2008, the entire contents of which are herein incorporated by reference . 
     BACKGROUND 
     The example embodiments disclosed herein relate to semiconductor devices, and more particularly, to an image sensor and a method of manufacturing the same. 
     An image sensor is a semiconductor device converting an optical image into an electric signal. An image sensor can be divided into a charge coupled device (CCD) and a CMOS image sensor (CIS). 
     The CCD includes MOS capacitors disposed to be adjacent to each other. The CCD is a device that a charge carrier is stored and moved by the capacitors. The CIS includes MOS transistors of as much as the number of pixels. The CIS is a device using a switching method sequentially detecting an output using the MOS transistors. 
     The image sensors include a shading layer for preventing a light from inputting in a specified region. The shading layer is formed of metal material and is disposed at a region which does not detect a light except upper portions of photodetectors. 
     SUMMARY 
     Example embodiments provide an image sensor. The image sensor may include a substrate including an effective pixel region and an ineffective pixel region adjacent to the effective pixel region and a shading pattern over the ineffective pixel region of the substrate. The shading pattern includes one or more openings configured to prevent an incident light from penetrating to the ineffective pixel region. The openings have a dimension through which incident light does not pass. The openings are also configured to pass hydrogen ions. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Example embodiments will be more clearly understood from the following brief description taken in conjunction with the accompanying drawings.  FIGS. 1-9  represent non-limiting, example embodiments as described herein. 
         FIG. 1  is a circuit diagram depicting a portion of an active pixel sensor (APS) of an image sensor according to example embodiments . 
         FIG. 2  is a drawing illustrating an image sensor according to example embodiments. 
         FIGS. 3A and 3B  are top plan views illustrating various examples of a shading layer pattern depicted in  FIG. 1 . 
         FIG. 4  is a graph representing a transmittance of a light according to a wavelength of a light. 
         FIG. 5  is a graph representing a width of an opening of a shading layer pattern according to a wavelength of a light and a refractive index of an interlayer insulating layer. 
         FIG. 6  is a flowchart illustrating a process of manufacture of an image sensor according to example embodiments. 
         FIG. 7  is a drawing illustrating an image sensor according to an example embodiment. 
         FIG. 8  is a drawing illustrating an image sensor according to an example embodiment. 
         FIG. 9  is a drawing illustrating an image sensor according to an example embodiment. 
     
    
    
     It should be noted that these Figures are intended to illustrate the general characteristics of methods, structure and/or materials utilized in certain example embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties encompassed by example embodiments. For example, the relative thicknesses and positioning of molecules, layers, regions and/or structural elements may be reduced or exaggerated for clarity. The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature. 
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Example embodiments will be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments are shown. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first region/layer could be termed a second region/layer, and, similarly, a second region/layer could be termed a first region/layer without departing from the teachings of the disclosure. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Example embodiments may be described with reference to cross-sectional illustrations, which are schematic illustrations of idealized example embodiments . As such, variations from the shapes of the illustrations, as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present invention should not be construed as limited to the particular shapes of regions illustrated herein, but are to include deviations in shapes that result from, e.g., manufacturing. For example, a region illustrated as a rectangle may have rounded or curved features. Thus, the regions illustrated in the figures are schematic in nature and are not intended to limit the scope of the present invention. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present application, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     In the drawings, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when an element such as a layer, region or substrate is referred to as being “on” or “onto” another element, it may lie directly on the other element or intervening elements or layers may also be present. Like reference numerals refer to like elements throughout the specification. 
     Spatially relatively terms, such as “beneath,” “below,” “above,” “upper,” “top,” “bottom” and the like, may be used to describe an element and/or feature&#39;s relationship to another element(s) and/or feature(s) as, for example, illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and/or operation in addition to the orientation depicted in the figures. For example, when the device in the figures is turned over, elements described as below and/or beneath other elements or features would then be oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. As used herein, “height” refers to a direction that is generally orthogonal to the faces of a substrate. 
     Referring to  FIGS. 1 and 2 , an image sensor  100  in accordance with example embodiments may include a semiconductor device converting an image into an electric signal. For example, the image sensor  100  may be a CMOS image sensor (CIS). The image sensor  100  may include an active pixel sensor (APS) array region on which pixels are disposed and a logic region (not shown) controlling the APS array region. 
     The APS array region may be driven by receiving various drive signals such as a pixel select signal (SEL(i)), a reset signal (RX(i)) and a charge transmitting signal (TX(i)) from a row driver (not shown). A plurality of pixels may be two dimensional in the APS array region. Each of the pixels may include a photodetector  110 , a detector  111  receiving charges accumulated in the photodetector and then storing the charges, a charge transfer device  112  transferring the charges accumulated in the photodetector  110  to the detector  111  and a readout device reading an optical signal input to the photodetector  110 . 
     If the charge transfer device  112  transfers charges, a well driving signal (WD(i)) for lowering a potential of around the photodetector  110  may be provided. The readout device may include at least one transistor. For example, the readout device may include a reset transistor  113 , a drive transistor  114  and a select transistor  115 . The reset transistor  113  can periodically reset the detector  111 . A source of the reset transistor  113  is connected to the detector  111  and a drain of the reset transistor  113  is connected to a voltage (V DD ). The drive transistor  114  may amplify a change of an electric potential of the detector  111  and may output the change to an output line (Vout). The select transistor  115  selects a unit pixel to be readout by a row unit. 
     The image sensor  100  may include a substrate  101 . The substrate  101  may include an epitaxial layer  104  on a bulk substrate  102 . The substrate  101  may include an effective pixel region  116  and an ineffective pixel region  118 . The ineffective pixel region  118  may be provided to detect an optical black. 
     The photodetector  110  may be on the substrate  101 . The photodetector  110  may generate and accumulate charges corresponding to an incident light. The photodetector  110  may include any one of a photodiode, a phototransistor, a photo gate and a pinned photodiode. For example, the photodetector  110  may have a structure including photodiodes having different conductivity types from each other are stacked in the epitaxial layer  104 . The detector  111  may be spaced apart from the photodetector  110  in the epitaxial layer  104 . The readout device may be on the substrate  101 . 
     An interlayer insulating layer  120  may be on the substrate  101 . Interconnections  122  may be in the interlayer insulating layer  120 . The interconnections  122  may be electrically connected to the transistors. A hydrogen supply layer  130  may be on the interconnections  122 . The hydrogen supply layer  130  may include material including a large amount of hydrogen. For example, the hydrogen supply layer  130  may include any one of a silicon nitride layer and a silicon oxynitride layer. A color filter  140  may be on the hydrogen supply layer  130 . The color filter  140  may include a red color filter (R/C), a green color filter (G/C) and a blue color filter (B/C). A microlens  150  may be on the color filter  140 . The microlens  150  may correspond to the red color filter (RIC), the green color filter (G/C) and the blue color filter (B/C). 
     A shading member  200  may be on the ineffective pixel region  118  between the substrate  101  and the hydrogen supply layer  130 . The shading member  200  may prevent an incident light from moving to the ineffective region  118 . In addition, the shading member  200  may be used as a path through which hydrogen ions move from the hydrogen supply layer  130  to the substrate  101  when a hydrogen annealing process is performed. For example, the shading member  200  may include a shading pattern  210  having openings  220 . The shading pattern  210  may be on the interlayer insulating layer  120 . 
     The shading pattern  210  may cover an entire surface of the ineffective pixel region  118 . The shading pattern  210  may be a metal. For example, the shading pattern  210  may include at least one among titanium, tungsten, a tungsten nitride layer, tungsten titanium, nickel, aluminum and copper. The shading pattern  210  may be used as an interconnection electrically connected to at least one among the transistors  113 ,  114  and  115 . The openings  220  may be provided to have various shapes to the shading pattern  210 . 
     Referring to  FIG. 3A , the shading member  200  may include the shading pattern  210  having the openings  220  of a shape of a plurality of islands. For example, the openings  220  may have a square shape. The openings  220  may be spaced a uniform distance apart from each other in the shading pattern  210 . A width (W) of the openings  220  may be controlled so that an incident light is shaded while a movement of hydrogen ions is allowed. If a wavelength of an incident light is λ, a maximum width (W: a distance between corners facing each other) of the openings  220  may be controlled at less than about λ/2. Because an incident light having a wavelength of λ cannot pass through the openings  220 , the incident light may be shaded by the shading pattern  210 . 
     Also, as the openings  220  are controlled so as to allow a diffusion of hydrogen ions as much as possible, an efficiency of hydrogen diffusion of an annealing process which will be described later may be maximized. Thus, the width (W) of the openings  220  may be controlled to have a maximum width (e.g., λ/2) capable of shading an incident light. The openings  220  may have a round shape. If the opening  220  have a round shape, a diameter of the openings  220  may be controlled at less than about λ/2. 
     Referring to  FIG. 3B , for example, a shading member  200   a  may include a shading pattern  210   a  having openings  220   a  of a line shape. If the openings  220   a  have a line shape, the incident light may be provided to polarize in a direction perpendicular to a lengthwise direction of the openings  220   a.  A polarizing member (not shown) capable of polarizing the incident light such as a polarizing filter may be on the shading member  200   a.  The openings  220   a  may be parallel to each other at a regular interval in the shading pattern  210   a.    
     In addition, the openings  220   a  may be perpendicular to a vibration direction of a polarized incident light. A width (W 1 ) of the openings  220   a  may be controlled so that an incident light may be shaded while a movement of hydrogen ions is allowed. If a wavelength of an incident light is λ, the width (W 1 ) of the openings  220   a  may be controlled at less than about λ/2. Because an incident light having a wavelength of λ cannot pass through the openings  220   a,  the incident light may be shaded by the shading pattern  210 . As the openings  220   a  are controlled so as to allow a diffusion of hydrogen ions as much as possible, an efficiency of hydrogen diffusion of an annealing process, which will be described later, may be maximized. Thus, the width (W 1 ) of the openings  220   a  may be controlled to have a maximum width (e.g., λ/2) capable of shading an incident light. 
     Referring to  FIGS. 1 through 5 , the width (W, W 1 ) of the opening ( 220 ,  220   a ) may be controlled by a refractive index of the interlayer insulating layer  120  between the substrate  101  and the hydrogen supply layer  130 . For example, if the interlayer insulating layer  120  is a silicon oxide layer (e.g., SiO 2 ) and shades an incident light having a wavelength of more than about 600 nm, a red light (R) has a wavelength of about 600 nm, see  FIG. 4 , and a silicon oxide layer may have a refractive index of about 1.47, see  FIG. 5 . A wavelength of the red light (R) may be reduced to about 400 nm (600 nm/1.47) while the red light (R) passes through the silicon oxide layer. 
     Thus, if the interlayer insulating layer is a silicon oxide layer and a width (W, W 1 ) of the opening ( 220 ,  220   a ) is controlled at less than about 200 nm (400 nm/2), the red light (R) may be shaded by the opening ( 200 ,  200   a ). For example, when the interlayer insulating layer  120  is a silicon nitride layer (SiN) and the width (W, W 1 ) is controlled less than about 145 nm (600 nm/(2.07×2)), the red light (R) may be shaded by the opening  220 . For example, when the interlayer insulating layer  120  is a silicon oxynitride layer (SiON) and the width (W, W 1 ) is controlled less than about 109 nm (600 mm (2.76×2)), the red light (R) may be shaded by the opening  220 . 
     In a manner similar to the manner described above, when an incident light is a green light (G) and a blue light (B), the width (W, W 1 ) of the opening  220  may be controlled by considering a refractive index of the interlayer insulating layer  120 . For example, a wavelength of the green light (G) is about 550 nm and a wavelength of the blue light (B) is about 450 nm. Thus, when shading an incident light having a wavelength of more than about 550 nm, the width (W, W 1 ) may be controlled less than about half of a value that a wavelength of the green light (G) is divided by a refractive index (n) of the interlayer insulating layer  120 . When shading an incident light having a wavelength of about more than about 450 nm, the width (W, W 1 ) may be controlled less than half of a value that a wavelength of the blue light (B) is divided by a refractive index (n) of the interlayer insulating layer  120 . 
     A process of manufacturing an image sensor according to example embodiments is described in detail. The description of common features already described with respect to the image sensor  100  according to example embodiments may be omitted or simplified.  FIG. 6  is a flowchart illustrating a process of manufacture of an image sensor according to example embodiments. 
     Referring to  FIGS. 2 and 6 , a substrate  101  may be prepared (S 110 ). For example, an epitaxial layer  104  may be on a bulk substrate  102 . Forming the epitaxial layer  104  may include a process of implanting an impurity ion into the substrate  101 . 
     An electric device may be on the substrate  101  (S 120 ). For example, a photodetector  110  may be on the epitaxial layer  104 . The photodetector  110  may be formed by performing ion implantation processes having different amounts of energy on the epitaxial layer  104 . Transistors (not shown) may be on the substrate  101 . 
     An interlayer insulating layer  120  and a shading member  200  may be formed (S 130 ). For example, the interlayer insulating layer  120  may be on the substrate  101 . The interlayer insulating layer  120  may include a plurality of sequential interlayer insulating layers on the substrate  101 . The interlayer insulating layer  120  may be any one material of a silicon oxide layer, a silicon nitride layer and a silicon oxynitirde layer. The shading member  200  may be on the interlayer insulating layer  120 . Forming the shading member  200  may include forming a metal layer on the interlayer insulating layer  120  and forming an opening on the metal layer by patterning the metal layer. As a result, a shading pattern having an opening  220  may be formed on the interlayer insulating layer  120 . 
     A hydrogen supply layer  130  may be formed (S 140 ). The hydrogen supply layer  130  may be of a material containing a large quantity of hydrogen. Forming the hydrogen supply layer  130  may include at least one of a silicon oxide layer, a silicon nitride layer and a silicon oxynitride layer on the interlayer insulating layer  120 . 
     A hydrogen annealing process may be performed on a resultant structure where the hydrogen supply layer  130  may be formed (S 150 ). Thus, a hydrogen ion may be diffused from the hydrogen supply layer  130  into the substrate  101 . An interface energy level by a dangling bond in the image sensor  100  may be reduced due to a diffusion of the hydrogen ion. The opening  220  may be provided so as to pass the hydrogen ion. Thus, when the hydrogen annealing process is performed, the hydrogen ion may also move from the hydrogen supply layer  130  to the substrate  101  through the opening  220 . 
     A color filter  140  and a microlens  150  may be formed (S 160 ). The color filter  140  may include a red color filter (R/C), a green color filter (G/C) and a blue color filter (B/C) on an effective pixel region  116  and an ineffective pixel region  118 . The microlens  150  may correspond to the red color filter (R/C), the green color filter (G/C) and the blue color filter (B/C). 
     As described above, the image sensor  100  according to an example embodiment may include the shading member  200  having an opening  220  which shades a light and allow a diffusion of a hydrogen ion at the same time. Thus, when the hydrogen annealing process is performed, example embodiments may prevent a diffusion of a hydrogen ion from being blocked and can improve an efficiency of the hydrogen annealing process using the shading member  200 . 
     Hereinafter, image sensors according to example embodiments are described in detail. The description of common features already described with respect to the image sensor  100  according to an example embodiment may be omitted or simplified. Also, a manufacturing process of image sensors according to the example embodiments is omitted because one of ordinary skill in the art can fully understand the manufacturing process of image sensors according to the example embodiments of the present invention through the manufacturing process of the image sensor according to an example embodiment. 
       FIG. 7  is a drawing illustrating an image sensor  100   a  according to an example embodiment. Referring to  FIG. 7 , the image sensor  100   a  according to an example embodiment may include a second shading member  300  compared with the image sensor  100  described referring to  FIG. 1 . For example, the image sensor  100   a  may include a substrate  101  including an effective pixel region  116  and an ineffective pixel region  118 , a first shading member  202  on the substrate  101  and the second shading member  300  on the first shading member  202 . 
     The substrate  101  may include an epitaxial layer  104  on a bulk substrate  102 . A photodetector  110  may be on the substrate  101 . In addition, a plurality of transistors (not shown) may be on the substrate  101 . An interlayer insulating layer  120  may be on the substrate  101 . An interconnection  122  electrically connected to the transistors may be in the interlayer insulating layer  120 . A hydrogen supply layer  130  may be on the interlayer insulating layer  120 . Color filters  140  may be on the hydrogen supply layer  130  located on the effective pixel region  116 . A microlens  150  may be on the color filters  140  and the second shading member  300 . 
     The first shading member  202  may be on the ineffective pixel region  118  between the substrate  101  and the hydrogen supply layer  130 . The first shading member  202  may have a similar structure to the shading member  200  described referring to  FIGS. 1 through 2C . The first shading member  202  may include a shading pattern  212  including an opening  222 . A width of the opening  222  may be controlled so as to shade a light and allow a diffusion of hydrogen. 
     The second shading member  300  may be on the hydrogen supply layer  130  of the ineffective pixel region  118 . The second shading member  300  may be used as an auxiliary shading member assisting a shading function of the first shading member  202 . For example, the second shading member  300  may include at least one color filter. The color filter may cover an entire surface of the interlayer insulating layer  120  of the ineffective pixel region  118 . The color filter may include any one of a red color filter, a green color filter and a blue color filter. Because the color filters have an own refractive index, a wavelength of a light passing through the color filters may be reduced. Thus, the second shading member  300  may prevent an incident light from moving to the substrate  101  and a width of the opening  220  of the first shading member  200  may be controlled by considering a refractive index of the second shading member  300 . 
     The image sensor  100   a  described above may include the second shading member  300  assisting a shading function of the first shading member  202  compared with the image sensor  100  according to an example embodiment. 
       FIG. 8  is a drawing illustrating an image sensor  100   b  according to an example embodiment. The image sensor  100   b  according to an example embodiment may include a second shading member  302  where a plurality of color filters are stacked compared with the image sensor  100  described referring to  FIG. 1 . For example, the image sensor  100   b  may include a substrate  101  including an effective pixel region  116  and an ineffective pixel region  118 , a first shading member  202  on the substrate  101  and a second shading member  302  on the first shading member  202 . 
     The substrate  101  may include an epitaxial layer  104  on a bulk substrate  102 . A photodetector  110  may be on the substrate  101 . In addition, a plurality of transistors (not shown) may be on the substrate  101 . 
     An interlayer insulating layer  120  may be on the substrate  101 . An interconnection  122  electrically connected to the transistors may be in the interlayer insulating layer  120 . A hydrogen supply layer  130  may be on the interlayer insulating layer  120 . Color filters  140  may be on the hydrogen supply layer  130  of the effective pixel region  116 . A microlens  150  may be on the color filters  140  and the second shading member  302 . 
     The first shading member  202  may be on the ineffective pixel region  118  between the substrate  101  and the hydrogen supply layer  130 . The first shading member  202  may have a similar structure to the shading member  200  described referring to  FIGS. 1 through 2C . The first shading member  202  may include a shading pattern  212  including an opening  222 . A width of the opening  222  may be controlled so as to shade a light and allow a diffusion of hydrogen. 
     The second shading member  302  may assist a shading function of the first shading member  202 . The second shading member  302  may include a color filter laminated structure. The color filter laminated structure may be on the hydrogen supply layer  130  located on the ineffective pixel region  118 . The color filter laminated structure may cover an entire surface of the ineffective pixel region  118 . The color filter laminated structure may have a structure in which a plurality of stacked color filters. For example, the color filter laminated structure may have a structure in which color filters of more than two of a red color filter, a green color filter and a blue color filter are stacked. Using the structure described above in which color filters of more than two are stacked as an auxiliary shading layer can increase a shading efficiency of the an auxiliary shading layer compared with a structure using one color filter as an auxiliary shading layer. 
       FIG. 9  is a drawing illustrating an image sensor  100   c  according to an example embodiment. The image sensor  100   c  according to an example embodiment may include a second shading member  204  on an effective pixel region compared with the image sensor  100  described referring to  FIG. 1 . For example, the image sensor  100   c  may include a substrate  101  including an effective pixel region  116  and an ineffective pixel region  118 , a first shading member  202  on the ineffective pixel region  118  and a second shading member  204  on the effective pixel region  116 . 
     The substrate  101  may include an epitaxial layer  104  on a bulk substrate  102 . A photodetector  110  may be on the substrate  101 . In addition, a plurality of transistors (not shown) may be on the substrate  101 . The effective pixel region  116  may include a region  116   a  detecting a light and a region  116   b  which does not detect a light. The region  116   a  detecting a light may be a region of the photodetector  110  of the substrate  101  and the region  116   b  which does not detect a light may be a peripheral region of the region  116   a.  The transistors may be on the region  116   b  which does not detect a light. 
     An interlayer insulating layer  120  may be on the substrate  101 . An interconnection  122  may be in the interlayer insulating layer  120 . A hydrogen supply layer  130  may be on the interlayer insulating layer  120 . Color filters  140  may be on the hydrogen supply layer  130 . A microlens  150  may be on the color filters  140 . 
     The first shading member  202  may be on the ineffective pixel region  118  between the substrate  101  and the hydrogen supply layer  130 . The first shading member  202  may have a similar structure to the shading member  200  described referring to  FIGS. 1 through 2C . The first shading member  202  may include a shading pattern  212  including an opening  222 . A width of the opening  222  may be controlled so as to shade a light and allow a diffusion of hydrogen at the same time. 
     The second shading member  204  may be on the region  116   b  of the effective pixel region  116  between the hydrogen supply layer  130  and the substrate  101 . The second shading member  204  may include a similar structure to the shading member  200  described referring to  FIGS. 1 through 2C . The second shading member  204  may include a shading pattern  214  having an opening  224 . The opening  224  may prevent an incident light from moving to the region  116   b  which does not detect a light. 
     The image sensor  100   c  according to an example embodiment may include the first shading member  202  preventing an incident light from moving to the ineffective pixel region  118  and the second shading member  204  preventing an incident light from moving to the region  116   b  of the effective pixel region  116 . 
     The foregoing is illustrative of example embodiments and is not to be construed as limiting thereof. Although example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the claims. It will be understood by one of ordinary skill in the art that variations in form and detail may be made therein without departing from the spirit and scope of the claims. The present invention is defined by the following claims, with equivalents of the claims to be included therein.