WO2018085242A1

WO2018085242A1 - Methods of characterizing glass panels during plasma processing

Info

Publication number: WO2018085242A1
Application number: PCT/US2017/059229
Authority: WO
Inventors: Robert George MANLEY; Piotr Janusz Wesolowski; Xi Xie
Original assignee: Corning Incorporated
Priority date: 2016-11-03
Filing date: 2017-10-31
Publication date: 2018-05-11
Also published as: TW201825433A

Abstract

Methods of characterizing a glass panel during a plasma-based treatment of the glass panel include capturing measurement digital images of at least a portion of the glass panel. The measurement digital images include a distorted reflection of the cathode from the glass panel surface due to a distorted surface shape of the glass panel. The distorted reflection of the cathode in the captured measurement digital images is used to estimate the surface shape of the glass panel that gives rise to the distorted reflection of the cathode. The estimated surface shape is used to identify at least one deformation of the glass panel. Moiré methods for measuring surface shape deformations of the glass panel during removal of the glass panel from the process chamber are also disclosed.

Description

METHODS OF CHARACTERIZING GLASS PANELS

DURING PLASMA PROCESSING

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.

Provisional Application Serial No. 62/416,838, filed on November 3, 2016, the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates to optical inspection of glass panels, and in particular relates to methods of cha racterizing glass panels du ring plasma processing.

BACKGROUND

[0003] Large sheets of glass ("glass panels") are used to form flat panel displays (FPDs). The glass panels need to be processed using a variety of microfabrication techniques such as cleaning, etching, depositing films (e.g., dielectric, metal and semiconductor films), and other surface treatments. Some of the processes utilize a plasma. An example plasma- based process is plasma-enhanced chemical vapor deposition (PECVD) for depositi ng films. Example PECVD films include S1O2, Si_xN_y, and amorphous silicon (a-Si). These films may be deposited on a bare glass su rface or over previously deposited patterned or u npatterned films.

[0004] The PECVD fil m deposition process is carried out in a vacuum chamber and at an elevated temperatu re. To optimize the economics of FPD manufactu ring, an entire glass panel (e.g. 2500 mm x 2250 mm) is patterned, assembled (matched with color filter) and then cut into smaller panels.

[0005] Unfortunately, the plasma of the PECVD process can interact with the glass and films in non-ideal ways. For example, the interaction of the plasma with a conductive film can lead to localized heating and film uniformity issues. Electrostatic charge build-up can also occu r. These phenomena can resu lt in thermal and mechanical instabilities that can lead to thermal and mechanical ly induced stress and large shape deformations. In addition, pre- PECVD robot and pin movement can deform the glass panel and post-PECVD vertical movement using lifting pings can dynamically deform the glass panel glass due to gravity and can also induce electrostatic charges and cause glass in homogeneities, such as residual stresses, thickness variations, local vs. edge warp, etc.

[0006] It is therefore advantageous to be able to characterize the glass panel before, du ring and after the glass panel is processed in an PECVD chamber in order to non-destructively assess process-induced deformations of the glass panel.

SUMMARY

[0007] An aspect of the disclosu re is a method of characterizing a glass panel. The method includes the steps of: a) performing a plasma-based treatment of an upper su rface of the glass panel that resides proximate a cathode; b) during the plasma-based treatment, capturing measurement digital images of at least a portion of the glass panel, wherein the measurement digital images comprise a distorted reflection of the cathode from the upper surface of the glass panel due to a distorted surface shape of the upper su rface of the glass panel; c) esti mating the distorted surface shape of the upper su rface of the glass panel as a function of the distorted reflection of the cathode; and d) identifying at least one deformation of the glass panel using the estimated distorted su rface shape of the upper surface of the glass panel.

[0008] Another aspect of the disclosure is the method as described above, wherein the plasma treatment is performed in a chamber having a top section that includes the cathode, and wherein the method further includes: removing the top section of the chamber;

operably disposing a patterned target relative to the upper su rface of the glass panel to create a reflection Moire geometry; capturing a first digital image of the patterned target as reflected from the upper su rface of the glass panel as the glass panel is supported by an upper surface of a platen; capturing second digital images of the patterned ta rget as reflected from the upper surface of the glass panel while lifting the glass panel off of the upper surface of the platen; su perimposing the first digital image with the second digital images to form interferograms having a Moire pattern; and examining the Moire pattern to identify at least one region of maximu m bending of the glass panel.

[0009] Another aspect of the disclosure is a method of characterizing deformations in a glass panel. The method includes the steps of: a) performing a plasma-based treatment of an upper su rface of the glass panel that resides proximate a cathode; b) generating a reference digital image of the glass panel that comprises a su bstantia lly u ndistorted reflection of the cathode; c) during the plasma treatment, capturing measurement digital images of the glass panel that comprise a distorted reflection of the cathode due to a distorted surface shape of the upper surface of the glass pa nel; d) determi ning whether the upper surface of the glass panel is distorted as a function of a comparison between the substantial ly undistorted reflection of the cathode of the reference digital image and the distorted reflection of cathode in the captured measu rement digital images; and e) identifying the at least one deformation of the glass panel as a function of the

determination.

[0010] Another aspect of the disclosure is the method as described above, wherein step d) of the method includes: i) making an initial estimate of the distorted surface shape and generating therefrom a simulated reflection of the cathode that includes a simu lated line reflection; ii) determin ing an amount of error between the simulated line reflection and the corresponding line reflection of the at least one measurement digital image; iii) using the amount of error, making a new estimate of the distorted su rface shape that reduces the amount of error; and iv) repeating i) through iii) until in ii), the error is reduced to less than a select error tolerance.

[0011] Additional features and advantages are set forth in the Detailed Description that follows, and in part will be read ily apparent to those skil led in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as wel l as the appended d rawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exempla ry, and are intended to provide a n overview or framework to understand the natu re and character of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings are included to provide a further understand ing, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the Detailed Description serve to explain principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the fol lowing Detailed Description, taken in conjunction with the accompanying Figu res, in which:

[0013] FIG. 1A is an elevated view of an example glass panel;

[0014] FIG. IB is a simila r to FIG. 1A and also shows an example transport device used to lift and move the glass panel;

[0015] FIG. 2A is a top-down view of an example susceptor used to support the glass panel in a processing chamber;

[0016] FIGS. 2B th rough 2D are side views of the glass panel being delivered onto and supported by lifting pins of the susceptor (FIGS. 2B, 2C) and then supported by the upper surface of the platen (FIG. 2D);

[0017] FIG. 3 is a contou r plot of the simulated surface shape of the glass panel when supported by the lifting pins of the susceptor, showing how the lifting pins can deform the surface shape, with the vertica l scale being exaggerated for ease of illustration;

[0018] FIG. 4A is a schematic diagram of an example optical monitoring and inspection system as operably a rranged relative to a processing chamber of a plasma-based treatment system;

[0019] FIG. 4B is a more detailed cut-away view of the optical monitoring and inspection system and the plasma-based treatment system of FIG. 4A;

[0020] FIG. 4C is a cross-sectional view (y-z plane) of the plasma-based treatment system shown in the form of a PECVD system;

[0021] FIG. 5A is a side view of the cathode of the PECVD system and also includes a close- up inset ISl of a portion of the lower surface of the cathode that shows a portion of an array of passages in the cathode;

[0022] FIG. 5B shows an angled view of the portion of the array of passages as shown in the close-u p inset of FIG. 5A, il lustrating how the array of passages can appear as lines when the array is viewed at an angle;

[0023] FIG. 5C is an example grazing-angle view of the cathode looking in the y-direction and also upward at the lower surface of the cathode and showing how the passages in the array appear as lines that run in the y-direction and the body portion of the cathode defines spaces between the lines;

[0024] FIG. 6 is a cross-sectional schematic diagram of the chamber illustrating the relatively la rge aspect ratio of the chamber;

[0025] FIG. 7A is a schematic il lustration of a perfect digital image wherein the line reflections are perfectly straight because the upper surface of the glass panel is perfectly flat;

[0026] FIG. 7B is a schematic illustration of an "actual" or measurement digital image that includes deviations in the otherwise straight line reflections due to variations in the shape of the glass panel;

[0027] FIG. 7C is a schematic il lustration of a simulated digital image based on an estimate of the surface shape from the measurement digital image;

[0028] FIG. 7D is a close up view of two corresponding line reflections for the simulated and measurement digital images illustrating an example of how a difference Δ between a given simulated line reflection and a corresponding actual (measured) line reflection can be measured in an x-y plane;

[0029] FIG. 8 is a schematic diagram of a coordinate system for the chamber that shows parameters that can be used in performing a triangulation calculation used in estimating the surface shape of the glass panel;

[0030] FIG. 9A is a schematic representation of a measured digital image based on an actual captured measu rement digital image and shows both the cathode and the reflection of the cathode, wherein the cathode reflection is distorted and includes a deformation region that has a deformation in the form of a wrinkle or ridge;

[0031] FIG. 9B is a plot of the height z (mm) versus y direction (mm) showing how the method of estimating the surface shape reveals that the deformation in the deformation region of FIG. 9A corresponds to a change in su rface height of the of glass panel of about 0.27 mm; [0032] FIGS. 10A and 10B are cross-sectional views of the PECVD system showing the chamber with the upper section removed and showing a patterned target operably arranged relative to the glass panel;

[0033] FIG. 11A is an elevated view of the glass panel and patterned target, along with the digital video camera and light source, illustrating the basic reflection Moire configuration of FIG. 10A;

[0034] FIG. 11B is similar to FIG. 11A and corresponds to the configu ration of FIG. 10B and schematically illustrates the deformation of the glass panel as caused by the central lifting pins of the susceptor du ring vertical transportation of the glass panel;

[0035] FIGS. 12A and 12B are front-on views of example patterned targets that can be used for the reflection Moire configu ration of the optical monitoring and inspection system; and

[0036] FIG. 13 is a schematic il lustration of an example set of interferograms formed by superim posing the reference digital image with measu rement digital images using the reflection Moire configuration of the optical monitoring and inspection system of FIGS. 10A, 10B, 11A and 11B, wherein the interferograms each includes a Moire pattern, with the where the Moire fringes on the t = n interferogra m illustrating a high-curvatu re portion (deformation) of the glass panel surface associated with the location of a lifting pin.

DETAILED DESCRIPTION

[0037] Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the d rawings to refer to the same or like parts. The d rawings are not necessarily to scale, and one skil led in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure.

[0038] The clai ms as set forth below are incorporated into and constitute part of this Detailed Description.

[0039] Cartesian coordinates are shown in some of the Figures for the sake of reference and are not intended to be limiting as to direction or orientation or system configu ration. [0040] The term "characterizing" in connection with the glass panel includes determining at least one property or characteristic of the glass panel, such as surface shape (topography), cracks, wrin kles, stress, changes in stress, changes in su rface shape, localized surface deformations, refractive index variations, variations in homogeneity, warping, etc.

[0041] The term "deformation" in connection with the glass panel includes any

characteristic of the glass panel that describes a difference in the glass panel from its ideal shape or cond ition, and in particularly includes such differences that render the glass panel unsatisfactory for subsequent use in a flat-panel device.

[0042] The term "plasma process" as used herein includes th ree distinct phases: a delivery phase where the glass panel is delivered to the plasma-based treatment system; a plasma treatment phase where the glass panel is subjected to a plasma-based treatment by the plasma-based treatment system; and a removal phase where the glass panel is removed from the plasma-based treatment system. The delivery and removal phases constitute tra nsportation phases.

[0043] The term "digital image" means an image captured using an electronic image sensor (e.g., as pa rt of a digital camera) that has discrete sensing elements (pixels), such as a CCD array or CMOS array.

[0044] The term "digital images" includes a sequence of digital images captu red by a digital imaging device such as a digital video camera or a digital camera when running in either video mode or in a fast-image-capture mode (e.g., 15 frames per second). A digital video camera is typically capable of captu ring digital images in video mode at a higher frame rate (e.g., 25 frames per second or 30 frames per second) than a digita l camera operating in either video mode or fast-image-capture mode. Digital video cameras also have other featu res that ma ke the image processing more efficient.

[0045] The terms "vertical" and "horizontal" may be used below to indicate a direction relative to the given coordinate system, where "vertical" is along the z-direction means along the direction of gravity, while horizontal means in the x or y direction or in the (x,y) plane perpendicu lar to the direction of gravity, unless otherwise indicated.

[0046] Glass panel [0047] FIG. 1A is an elevated view of an example glass panel 10 that is shown residing in an x-y plane. The glass panel 10 is in the form of a sheet having an upper surface 12, a lower surface 14 and sides 16. The glass panel 10 has respective (x,y) dimensions LX and LY, and a thickness TH. In an example, dimensions LX and LY can each be greater than 1 meter or even greater than 2 meters. In an example, the thickness TH is on the order of 0.3 millimeters to 0.7 millimeters. A reference featu re 18, such as a fiducial, indicia, mark, etc., is shown on the upper surface 12. The reference feature 18 can be placed at a known (i.e., precise) location on the glass panel 10 and/or elsewhere to establish one or more reference positions or coordinates when performing image processing, as described in detail below.

[0048] FIG. IB is similar to FIG. 1A and further shows an example transport device 30 that can be used to transport (i.e., lift and move) the glass panel 10, e.g., as part of a robotic arm. The transport device 30 includes a base 32 with a number of prongs 34 each having a flat surface 36. The prongs 34 extend outwardly from one side of the base and support the glass panel on flat su rfaces 36. The arrow AR is used to show a direction of movement towards a processing chamber not shown in FIG. IB but that is introduced and described below.

[0049] The transport device 30 can be used to transport the glass panel 10 from a storage location to a support device within the aforesaid processing chamber as part of a delivery phase of a plasma treatment. FIG. 2A is a top-down view of an example support device 40 in the form of a susceptor (hereinafter, susceptor 40) configu red to operably support glass panel 10. The susceptor 40 is part of a plasma-based treatment system, described below, that includes a processing chamber 210 defined by walls 214 and having a cham ber interior 216. The processing cham ber 210 includes a door 219 at one end of the processing chamber (e.g., on the right side as shown in FIG. 2A). The susceptor 40 resides within the chamber interior 216 includes a platen 41 having a flat upper surface 42. The susceptor 40 also includes a number of lifting pins 44 that reside in slots 46. In an example, the platen 41 is movable in the z-direction relative to lifting pins 44. The arrow AR shows the direction in which the glass panel 10 is transported into chamber interior 216 through door 219 (see FIG. IB). The other components of FIGS. 2A are introduced and discussed below.

[0050] FIG. 2B is a side view of the susceptor 40 showing the lifting pins 44 extending above the platen upper surface 42 and ready to receive the glass panel 10, which is supported by the prongs 34 of the transport device 30. The precise configuration (i.e., nu mber and spatial distribution) of the lifting pins 44 depends on the size of the particular glass panel 10.

[0051] FIG. 2C is similar to FIG. 2B and shows the glass panel 10 supported by the lifting pins 44 above the upper su rface 42 of the susceptor 40. FIG. 2D is similar to FIG. 2C and shows the lifting pins 44 in their retracted position by moving the platen 41 in the + z direction, as il lustrated by arrow AZ in FIG. 2C so that glass panel 10 is supported by the upper su rface 42 of the susceptor 40. In an example, the platen 41 is heated, e.g., by one or more heating elements (not shown) within the platen 41.

[0052] Thus, in an example, the glass panel 10 initially resides in a room-tem peratu re storage location that is u nder vacuum. The glass panel 10 is lifted therefrom and moved to and deposited upon the lifting pins 44 of the susceptor 40 du ring the delivery phase of the plasma processing. The glass panel 10 is then lowered onto the upper surface 42 of the platen 41. The temperature of the interior 216 of the processing chamber 210 is then ramped up a process temperatu re (e.g., 300 C) as part of a plasma treatment phase of the plasma processing

[0053] After the plasma treatment, the temperature of the interior 216 of the processing chamber 210 ramps back down to room temperatu re. The processed glass panel 10 is then lifted from the susceptor upper surface 42 by the lifting pins 44. The transport device 30 is then used to lift and carry the processed glass panel 10 out of the processing chamber 210 (e.g., th rough door 219) and to another post-process storage location as part of a removal phase of the plasma processing. In an example, the pre-process storage location, the processing chamber 210 and the post-storage location are all under vacuu m (e.g., in a cluster-tool configuration) so that the glass panel 10 remains in a vacuum for the entire plasma processing operation.

[0054] Du ring these different phases of the plasma processing, the glass panel 10 is subjected to mechanical and thermal deformation forces. FIG. 3 is a contou r plot of the simulated su rface shape (deformation) of the upper surface 12 of the glass panel 10 when supported by the lifting pins 44 of the susceptor 40. The lifting pins 44 include in the example configu ration a central array of two rows of three lifting pins and an outside array of sixteen lifting pins arranged adjacent the perimeter of the platen 41. Other configurations can be used. The vertical scale of FIG. 3 is exaggerated for ease of il lustration. The six central peaks PC and the elevated perimeter EP in the contou r plot show how the lifting pins 44 can deform the glass panel 10. Computer simu lations show that the magnitude of the deformation of the glass panel 10 (i.e., the peak-to-val ley distance) due to lifti ng by the lifting pins 44 can be as large as 1.5 millimeters for a glass panel having a thickness TH of 0.5 millimeters.

[0055] Consequently, the glass panel 10 is preferably monitored du ring the entire plasma processing— i.e. du ring the delivery phase, the plasma treatment phase and the removal phase - to characterize the glass panel to determine if one or more of these phases have causes a deformation in the glass panel.

[0056] Optical monitoring system

[0057] FIG. 4A is a top-down schematic diagram of example optical monitoring system ("monitoring system") 100 for monitoring and characterizing the glass panel 10. The monitoring system 100 is operably arranged relative to a plasma-based treatment system ("treatment system") 200 such as a PECVD system. FIG. 4B is similar to FIG. 4A and shows a more detailed cut-away view in the x-y plane of the treatment system 200. FIG. 4C is a close-u p cross-sectional view in the y-z plane of the treatment system 200, which is configured by way of example as a PECVD system. The discussion below is based on the treatment system 200 in the form of a PECVD system by way of example. Other configurations of the monitoring system 100 besides those shown in FIGS. 4A th rough 4C can also be employed.

[0058] The treatment system 200 includes the aforementioned processing chamber 210. At least one wall 214 includes one or more windows 218 (e.g., fou r windows) such as arranged as shown in FIGS. 4A and 4B as wel l as in FIG. 2A. The processing chamber 210 has a top section 211T and a bottom section 211B. As noted above, the processing chamber 210 can include the door 219 through which the glass panel 10 can be introduced into the chamber interior 216 and disposed onto the susceptor 40 using the transport device 30. The chamber interior 216 has a length LCY in the y-direction, as shown in FIG. 4A.

[0059] In an exam ple, the treatment system 200 includes within interior 216 of the processing chamber 210 the aforementioned susceptor 40 as well as a cathode 220. The cathode has a lower surface 221 that resides above the susceptor upper su rface 42 and that is generally parallel thereto. The susceptor 40 supports the glass panel 10 on the upper surface 42. FIG. 4B shows the reference features 18 arranged in the chamber interior 216. The pu rpose of the reference features 18 is discussed below.

[0060] With reference to FIG. 4C, the susceptor 40 and cathode 220 are electrically connected to a radio-frequency (RF) unit 240, with the susceptor 40 serving as an anode. The activation of the RF unit 250 forms a plasma 250 from gas 232. The plasma 250 interacts with the upper surface 12 of the glass panel 10 to as part of a plasma processing step, e.g., a deposition step, an etch step, a cleaning step, etc.

[0061] FIG. 5A is a side view of an example cathode 220. The cathode 220 includes a body or platen 223 that has the aforementioned lower surface 221. The cathode 220 includes an array 222A of passages 220 that ru n through the platen 223 in the z-direction. The passages 222 allow gas 232 from a gas source 230 to pass through the cathode platen 223 and diffuse into the space between the susceptor 40 and the cathode (see FIG. 4C). Thus, cathode 220 also serves as a gas diffuser.

[0062] The close-u p inset IS1 of FIG. 5A shows a portion of the lower su rface 221 of the cathode 220 as seen looking in the +z direction (i.e., the upward direction). The close-u p inset II shows a portion of the a rray 222A of passages 222. The passages 222 are relatively small and are arranged a long the x and y directions. In this configuration, the passages 222 appea r as dark lines while the remaining portion of lower su rface 221 defined by platen 223 appear as light spaces 224 when viewed at an increasing grazing viewing angle, as illustrated in the angled view of the portion of array 220A of FIG. 5B. Thus, in the discussion below, the lines formed by the passages are referred to as "lines 222."

[0063] FIG. 5C is an example view of how the lower su rface 221 of cathode 220 appears when viewed upward ly at a grazing angle along the y-direction. The view is the same when looking along the x-direction due to the x-y symmetry of array of passages 222A. Thus, when viewed at a grazing angle in the x-direction or the y-direction, the lower su rface 221 of cathode 220 has the appearance of a large grating with lines 222 and spaces 224. In an example, a grazing viewing angle is greater than 60 degrees relative to normal incidence (i.e., normal incidence = 0 degrees). [0064] The cathode 220 resides at a height h above susceptor u pper su rface 42. In an example, the height h is between 25 millimeters and 100 millimeters, while the length LCY of the chamber interior is on the order of 2 meters or so. Thus, the chamber interior 216 has a relatively large aspect ratio LCY:h. For example, for h = 0.1 meters and LCY = 2 meters, the aspect ratio is 2/0.1 = 20. For h = 0.025 meters and LCY = 2 meters, the aspect ratio is 2/0.025 = 80.

[0065] With reference again to FIGS. 4A through 4C, monitoring system 100 includes at least one light sou rce 110, with each light source 110 operably disposed adjacent one window 218. Each light source 110 emits light 112, which is used to illuminate interior 216 and glass panel 10 residing therein when plasma 250 is not present. The light sources 110 are operably connected to a light-source controller 120.

[0066] The monitoring system 100 also includes one or more digital imaging devices 130 that capture digital images. The digital imaging devices 130 are operably connected to an image acquisition unit 140, which in turn is operably connected to an image processing unit 150. In a preferred embodiment, the digital imaging devices 130 are digita l video cameras that capture digital video images. Thus, in the discussion below, the digital imaging devices 130 are referred to as digital video cameras 130.

[0067] In the example configuration shown in FIGS. 4A and 4B and also in FIG. 2A, a first digital video camera 130 is arranged between two light sources 110 at the wall 214 opposite door 219, while a second digital camera is arranged on the adjacent wal l (e.g., the right-side wal l in FIGS. 4A and 4B) relatively close to the wal l where the first camera and the two light sou rces 110 reside. Thus, in an example, the first and second digital video cameras are arranged at right angles to one another, i.e., they view glass panel 10 from first and second viewing directions VDl and VD2 that are perpendicular to each other, as shown in FIG. 4B as wel l as in FIG. 2A.

[0068] Each digital video camera 130 is disposed adjacent one of windows 218 to capture digital images of glass panel 10 residing within interior 116 of processing chamber 210. Each of the captu red digital images includes the reflection of cathode 220, as described in greater detail below. This is made possible by the small viewing angles (relative to the horizontal) due to the aforementioned large aspect ratio L:h of chamber interior 216. In an example, the digital video cameras 130 are configured for wide-angle viewing, e.g., by having wide-angle lenses 131. The wide-angle viewing (i.e., field of view) of the two example digital video cameras 130 is illustrated by the viewing lines VL, shown as dotted lines for one digital video camera and as dashed lines for the other digital video camera. The area of overlap of the viewing lines VL for the different digital video cameras 130 indicates the area of the glass panel 10 that can be seen by both digital video cameras. It is noted that the viewing lines VL and their angles are not to scale and are shown for the sake of explanation on ly.

[0069] In an example, each digital video camera 130 has an image sensor 133 (see FIG. 4C) with a resolution of 1920 x 1080 pixels (16:9), with a pixel size of 5.5 microns and an overall dimension of 10.56 mm x 5.94 mm. Other configurations of image sensor 133 can also be used.

[0070] FIG. 6 is a schematic cross-sectional view of the processing chamber 210 and the digital video camera 130 that, though not exactly to scale, illustrates the relatively large aspect ratio LCY:h of the processing chamber. The digital video camera 130 is general ly arranged to view the midd le of the chamber interior 216, i.e., is disposed at h/2. For h/2 = 34 millimeters/2 = 17 millimeters and for a length LCY = 2500 millimeters, the reflection angle Θ (relative to vertical) from the u pper su rface 12 of the glass panel 10 is between about 80 degrees and 89 degrees. In this angula r range, the reflecta nce of the glass panel 10 is greater than 60%. When the reflection angle Θ is 85 degrees or greater, the reflectance from the glass panel 10 is 70% or greater.

[0071] Digital image capture during plasma treatment

[0072] An aspect of systems and methods disclosed herein includes captu ring digital images of the glass panel 10 du ring plasma treatment of the glass panel i n the treatment system 200 using the monitoring system 100.

[0073] In this example where digital images are captured during the plasma treatment phase, the light sources 110 may not be needed due to illumination of the interior 216 of processing chamber 210 by plasma 250. In an example, the digital video cameras 130 can include an optical filter F to filter select wavelengths of the light emitted by the plasma 250 to improve the quality of the digital images. For example, some plasmas emit light that has a pink tint and the optical filter F can be used to remove red wavelengths from the digital images to provide better color balance. The optical filter F can also be configu red to filter out at least one of UV and IR light, as well as at least one select polarization of light to improve imaging contrast.

[0074] The plasma 250 can serve as a relatively bright source of illumination of the chamber interior 216, thereby allowing for relative short exposures, e.g., on the order of 3 milliseconds (ms). The exposu re time for each digital image can be controlled by each digital video camera 130, e.g., by software therein.

[0075] In an example of the operation of the monitoring system 100, the glass panel 10 is removed from a storage location, transported to the treatment system 200 and placed on the lifting pins 44 of the susceptor 40 using the transport device 30, as part of the delivery phase of the plasma process. The platen 41 is then raised so that the glass panel 10 is received (e.g., th rough door 219) and then supported in the chamber interior 216 on the upper surface 42 of the platen.

[0076] Once the glass panel 10 is thus operably arranged, the plasma treatment is initiated in the treatment system 200 to treat (process) the upper surface 12 of the glass panel. Meanwhile, the treatment system 100 is activated to capture digital images of the upper surface 12 of the glass panel 10. In an example, the settings of the digital video cameras 130 (e.g., exposu re time, filter type, etc.) can be adjusted while the optional optical filter F can be chosen for the particular il lumination characteristics of plasma 250, such as intensity and output spectru m (color/wavelength).

[0077] As noted above and as discussed in greater detail below, the digital images 132 from the digital video cameras 130 show the lines 222 of cathode 220 as reflected from upper surface 12 of glass panel 10. FIG. 7A is a schematic illustration of a reference digital image 132P that is "perfect" or "ideal," i.e., one where glass panel 10 is undistorted. The digital image 132 general ly includes an image lOi of glass panel 10, and in particular includes an image 12i of upper su rface 12. The idealized digital image 132P also shows a cathode image 220R that includes perfectly straight line reflections 222R and perfectly straight space reflections 224R due to perfect specular reflection of cathode lines 222 and spaces 224 from a perfectly smooth upper su rface 12 of an ideal glass panel. [0078] FIG. 7B is similar to FIG. 7A and is a schematic illustration of an "actual" or

"measu rement" digita l image 132M wherein the line reflections 222R and space reflections 224 of the cathode image 220R are substantially distorted due to the upper su rface 12 of the glass panel 10 being substantially distorted, i.e., the upper surface has a substantial ly distorted surface shape. The distorted shape of the upper su rface 12 can be due to the plasma process and/or from transporting glass panel 10. The distorted surface shape ca n include deformations that manifest as substantial changes or deviations in the topography of upper surface 12 relative to a substantially planar (i.e., substa ntially undistorted) reference su rface. I n an example, the distorted shape of the upper surface 12 is due to local deformations (e.g., sag, bending, etc.) in the glass panel 10. The distorted shape of the upper surface 12 of the glass panel 10 can also be due to thickness variations. Thus, topography variations in the upper surface 12 of the glass panel 10 can cause corresponding deformations in the line reflections 222R and space reflections 224R. In the discussion below, reference is made to the line reflections 22R while reference to the space reflections 224 is generally omitted for ease of explanation.

[0079] In an exam ple, at least one reference digital image 132R is captured for calibrating monitoring system 100. The reference digital image 132R can be obtained by placing a thick glass su bstrate or even a mirror on the susceptor 40. The reference digita l image 132R can be similar to the ideal digital image 132P, as indicated in FIG. 7A. The reference digital image 132R need not be perfect like perfect digital image 132P of FIG. 7A and can generated by a surface that is su bstantially u ndistorted, i.e., one that includes small amounts of distortion (e.g., within 2% or within 1%) relative to perfectly flat su rface. In another example, the reference digital image 132R can be a simulated image obtained by com puter modeling, e.g., using com mercially available ray-tracing softwa re.

[0080] Once the plasma treatment of the glass panel 10 is completed, the glass panel is removed from the processing chamber 210 using the transportation device 30 as described above. Electrostatic charges can develop between the glass panel 10 and the susceptor 40 du ring the PECVD process that can have an impact on the removal of the glass panel 10. The electrostatic charges create an attractive force between the susceptor upper su rface 42 and the lower su rface 14 of the glass panel 10. The lifting pins 44, in addition to the gravitation force, now also have to overcome the attractive electrostatic force, which amplifies the deformation of the portions of the glass panel 10 that reside directly above the lifting pins 44 (see FIG. 3).

[0081] Once the reference and measu rement digital images 132R and 132M are obtained, the measurement digital images are processed using the imaging process u nit 150 to characterize the glass panel 10. This includes identifying at least one deformation in the glass panel, and can further include determining the location of the at least one defect and fu rther include determining the size and shape of the at least one defect.

[0082] In an example, the imaging process unit 150 includes instructions embodied in a non-tra nsitory computer-readable mediu m to carry out the image processing methods described herein .

[0083] In an example, the image processing methods includes a calibration step that utilizes the reference digital image 132R. The reference digital image 132R provides geometrical parameters to be used in processing the actual captured digital images. I n an example, the reference digital images 132R can include images of one or more reference featu re 18 placed on glass panel 10 (see FIG. 1A) or on a reference substrate or within interior 216 of processing chamber 210 (see FIG. 4B). The reference features 18 provide a precise location for any deformations that are identified du ring the image processing method. In another example, the calibration step is not included, e.g., when the location of deformations can be adequately determined from the measurement images 132M.

[0084] In an example, processing of the measurement digital images 132M to characterize the glass panel 10 involves gradient estimation and numerical integration. Based on select featu res in the interior 216 of processing chamber 210 (e.g., reference featu res 18), triangulation can first be used to estimate the location and overall shape of any

deformations. This observation/estimate is then used to sim ply the original 3-D surface- shape analysis into a 2-D problem along a selected line of interest, such as along one of the line reflections 222R.

[0085] The accuracy of the first step is enhanced by using reference featu res 18 with in interior 216 of processing chamber 210 to reduce the impact from measu rement errors. The reference features 18 can be featu res that already exist within chamber interior 216, such has holes or ma rks on chamber walls 214. The reference featu res 18 can also be marks, fiducials, etc. that are added to the chamber interior 210 or to the glass panel 10. Each reference featu re 18 can also be verified against another reference featu re to ensure a proper esti mate. This calibration step compensates for or otherwise reduces imaging im perfections.

[0086] Once the glass panel 10 is characterized, then assumptions can be made as to the location, size and shape of any deformation found, such as its orientation a nd possible reference points on a specific line of interest. With these assumptions, the size and shape of the deformation (e.g. a particular type of su rface deformation such as a wrin kle) can be esti mated along one or more selected lines, such as along one or more line reflections 222R.

[0087] Thus, in an example, once the (optional) calibration step is completed, a

measurement digital image 132M of interest is uploaded into the image processing unit 150. The characterization process then includes making an initial estimate of the su rface shape (topography) SS_E(x,y) of upper su rface 12 of the glass panel 10. This initial estimate of SS_E(x,y) can be made based on the configuration of the line reflections 222R in the measurement digital image 132M as compared to those of the reference digita l image 132R or to an assu med "perfect" reference imaged generated by simulation and stored in the image processing unit 150. The line reflections 222R in the reference digital image 132 can thus serve as reference lines. Computer simulation (e.g., ray tracing) can be performed to generate a set of line reflections 222R in the reference digital image 132 based on common surface shapes that arise during plasma treatment. Thus, the reference lines in the reference digital image 132 need not be perfectly straight.

[0088] The initial estimate of the surface shape SS_E(x,y) of the upper surface 12 of the glass panel 10 is then used to generate a simulated digital image 132S, as shown in FIG. 7C. This simulated digital image 132S is then compared to the measurement digital image 132M and the differences measured, i.e., a difference Δ between corresponding line reflections 222R in the simulated and measu rement digital images. Based on the measured differences, a new estimate of the surface shape SS_E(x,y) of upper su rface 12 is generated and an updated simulated digital image 132S is generated. The difference Δ between the u pdated simu lated digital image 132S and the measurement digital image 132M is once again determined. The new estimated surface shape SS_E(x,y) is selected to reduce the difference Δ. [0089] This process of determi ning the difference Δ between the simulated digital image and the measurement digital image by updating the surface shape estimate SS_E(x,y) is iterative, i.e., it is repeated until the difference Δ becomes sufficiently small, e.g. to within a tolerance T of 5% or to within a tolerance T of 2% or to within a tolerance T of 1% for example. The differences Δ between the updated si mulated digital image 132 and the measurement digital image 132M can be measured using any technique known in the art for measuring and/or characterizing differences between two lines. An example of such a tech nique is a least-mean-squares measu rement.

[0090] FIG. 7D is a close-up view of a select line reflection 222R (dotted line) from the measurement digital image 132M and the corresponding line reflection (solid line) from the simulated digital image 132S. The x, y coordinates used in FIG. 7D are not necessa rily those associated with processing chamber 210 and a re simply convenient coordinates used for image processing. One value of a difference Δ between the measurement and simulated digital images 132M and 132S is shown as Δ, by way of illustration. The difference Δ, is taken between a measu rement image location (x_im, y_im) and a corresponding simulated image location (χ,₅, y,_s) for the measurement and simulated digital images 132M and 132S, respectively. In an example, Δ, = [(x_im - x_is)² +(y_im - yi_S)²]^{1 2}- In an exam ple, Δ values are calcu lated for a large number of corresponding points (x_m,ym) and (x_s,y_s) along the line reflection 222R for the measurement and simu lated digital images 132M and 132S, respectively. Judicious selection of the origin and orientation of the x-y coordinate system can be used to facilitate the calculations of Δ.

[0091] The difference Δ ca n also be calculated for each line reflection 222R for the measurement and simulated digital images 132M and 132S to determine an overall or total difference measu rement Δτ for the entire simu lated digital image 132S and corresponding measurement digital image 132M.

[0092] Once the total difference measu rement Δ_τ is less than the select tolerance T (i.e., Δ_τ < T), the latest estimated surface shape SS_E(x,y) used to generate the latest simulated image is taken as the final or target su rface shape for the upper surface 12 of the glass panel 10.

[0093] The following example analysis can be carried out in an example of implementing the optimization method (algorithm) described above. First, each line reflection 222R is abstracted as a line of zero width at the line's center during the calculation. The location of a given line reflection 222R in the processing chamber 210 is then estimated by mapping its shape in the image to its shape in the actual chamber and onto the upper surface 12 of the glass panel 10.

[0094] FIG. 8 is a schematic diagram of a coordinate system that shows parameters used in performing a triangu lation calculation used in this mapping operation as part of the optimization method described above. For simplicity, an origin O of the coordinate system is set at the location of the digital video camera 130. There are a series of reference featu res 18 (e.g., holes) on at least one wall 214 of the chamber interior 216 and at positions H relative to origin O. One such reference feature 18 is shown for ease of explanation.

[0095] The position H of reference featu res 18 can be used for performing a geometry calibration, which in an example includes precisely establishing the position (pitch, yaw and roll) of digital video camera 130. The calibrated geometry is then used to map the position of the captured line reflections 222R. The coordinate system of FIG. 8 includes a ta rget plane TP = S-S', i.e., as defined between the points S and S'. The coordinate system also includes a reference plane RP = O-O', i.e., as defined by the origin O and a point O' on the wal l 214.

[0096] A point G is defined on the target plane TP by a line OG' from the origin O and that runs at a small angle a relative to the reference plane RP and that intersects the target plane at the point G while intersecting wall 214 at a point G'. For a small angle, a can defined as = O'OG = arctan(0'H/00')+ arctan(HG/00'), which can be calcu lated from a measurement of the chamber geometry. The distance y_G along the target plane TP to the point G is given by y_G = z_Tp /tan( ), with z_Tp being the distance from the reference plane RP to the target plane RP in the z-direction and thus to the point G (i.e., z_Tp = z_G). The remaining G-coordinate x_G can be calculated in a similar fashion to define the (x_G, y_G, z_G) coordinates for the point G relative to the origin O.

[0097] With the position information derived as described above, the orientation of the overall deformation on the glass panel 10 based on the captured line reflections 222R on the glass panel can then be estimated. This information can be used to simplify the calculation of the final (estimated) su rface shape SS_E(x,y) for the glass panel 10. When the surface shape has certain features, the mathematical formulas used to analyze the surface shape can be significantly reduced. One of these cases is where su rface shape SS_E(x,y) is constant along x axis, so that SS_E(x,y) = SS_E(y).

[0098] Simulations can be performed that take into account the geometry of the processing chamber 210 to generates simulated video images 132S given a select surface shape SS_E(x,y). The simulated video images 132S can then be used to estimate an actual surface shape SS(x,y) of the glass panel 10 as described above. The iterative numerical optimization procedu re described above estimates su rface sha pe SS_E(x,y) of the u pper su rface 12 of the glass panel 10 along the line reflections 222R. The physical location of the given line reflection 222R line is known from the geometry of processing chamber 210 together with the calibration of the digital image 132 per the coordinate system and parameters of FIG. 8. As there are multiple line reflections 222R in each digital image 132, multiple line reflections 222R can be evaluated. The result forms a mesh, representing the estimate three- dimensional su rface shape SS_E(x,y) of glass panel 10. The entire estimated surface shape SS_E(x,y) can be obtained by interpolation between the locations of line reflections 222R.

[0099] In another example, direct numerical methods can be used to solve for SS(x,y), such as described in U.S. Patent No. US 8441532 B2, entitled "Shape measurement of specu lar reflective surface," which is incorporated by reference herein. Because of the grazing viewing angles associated with the image capture process described herein, the

optimization approach described above may be more reliable than a direct calculation.

[00100] Once an acceptable final estimate SS_E(x,y) of the surface shape for the upper surface 12 of the glass panel 10 is obtained, it can be used to determine if the glass panel characteristics include a deformation or deformations that would prevent its use in a flat panel system or device.

[00101] FIG. 9A is a schematic representation of a measured digital image 132M based on an actual captured measurement digital image 132M. The measured digital image 132M shows the cathode 220 as well as the cathode reflection 220R from the upper surface 12 of the glass panel 10. The cathode reflection 220R is distorted and includes a deformation region 226 wherein the line reflections 222R have a deformation that appears as a "wrinkle" or ridge in the norma l (idea l) straight-line appeara nce. The deformation region 226 thus identifies a localized deformation in the form of localized warp/waviness in glass panel 10.

[00102] FIG. 9B is a plot of the height z (mm) versus y direction (mm) showing how the method of estimating the surface shape SS_E(x,y) reveals that the deformation of line reflection 222R in deformation region 226 corresponds to a change in su rface height of the upper surface 12 of the glass panel 10 of about 0.27 mm. This amount of change in the surface height over such a short distance confirms the su rface deformation in the deformation region 226.

[00103] The monitoring methods disclosed herein can be used to quantitatively monitor, for example, the interaction between metal lic film deposition and RF field that might have a detrimental effect during PECVD process onto a perfect flat glass su bstrate 10. More generally, the monitoring methods disclosed herein can be used for process control and quality control when plasma processing glass panels 10.

[00104] Digital image capture during glass panel transportation phases

[00105] As discussed above, in the delivery phase of the plasma process, the glass panel 10 is generally transported horizontally to the processing chamber 210 by the transport device 30 and then is transported through the door 219 and then lowered vertically into the chamber inside the processing chamber 210 and onto the vertically oriented lifting pins 44, and then onto the flat upper su rface 42 of the platen 41. This process is reversed in the removal phase.

[00106] Du ring transportation and insertion into the chamber interior 216, the glass panel 10 u ndergoes flexu ral deformations. These deformations can be transient. But even tra nsient deformation can result in damage to the glass panel 10, so that a fast non-contact measurement technique for measuring deformation is preferred. I n particular, tra nsient deformations that exceed the fractu re toughness of the glass panel are the most problematic because they may lead to glass breakage or cracking. Note that the transient deformations can be exacerbated by the aforementioned attractive electrostatic force between the glass panel 10 and the susceptor 40 that arises after processing the glass panel. Thus, monitoring of the transient deformation du ring the removal phase is of particu la r im portance. [00107] To closely study the transient deformation of the glass panel 10 during the removal phase of the transportation process, the top section 211T of the processing chamber 210 is removed. This includes removing the cathode 220. Thus, the cathode 220 is no longer available to serve as a grating to be reflected and captu red in the digital images 132 and used to cha racterize glass pa nel 10 and in particular to determine its surface shape SS(x,y). Likewise, plasma 250 is no longer available to provide bright il lumination of interior 216 of processing chamber 210.

[00108] Thus, to monitor the glass panel 10 during the removal phase, a patterned target is employed in monitoring system 100 in a manner that creates a reflection Moire imaging configuration. FIGS. 10A and 10B are schematic diagrams that illustrate an example of monitoring system 100 as modified to include a patterned target 300 operably arra nged relative u pper su rface 12 of glass panel 10. FIG. 11A is an elevated view of the glass panel 10 and the patterned target 300, along with the digital video camera 130 and light source 110, illustrating the basic reflection Moire configuration of FIG. 10A. FIG. 11B is similar to FIG. 11A and corresponds to the configuration of FIG. 10B and schematically ill ustrates the deformation of the glass panel 10 as caused by the central lifting pins 44 of the susceptor 40 du ring transportation of the glass panel. Cartesia n coordinates (Χ', Υ', Ζ') are employed in FIGS. 10A, 10B and 11A, 11B for reference.

[00109] Since the plasma 250 is no longer available for illumination, the one or more illumination sources 110 can be employed to substantially uniformly il luminate the patterned ta rget 300 with light 112. The one or more illumination sources 110 ca n also be moved into different positions since they do not need to illuminate the chamber interior 216 through windows 218. In an example, the digital video cameras 130 can utilize a high- defin ition image sensor 133, e.g., having 24 megapixel resolution.

[00110] FIGS. 12A and 12B are front-on views of two exam ples of the patterned ta rget 300. The patterned target 300 has a pattern 302. The example pattern 302 of the patterned target 300 of FIG. 12A is in the form of a grid. The example pattern 302 of the patterned ta rget 300 of FIG. 12B is in the form of vertical lines. The pattern 302 can be different, e.g., can be horizontal lines, concentric circles, etc. In an example, the patterned target 300 comprises a display (e.g., and LCD display) where the pattern 302 can be selected from a number of different patterns, and can be changed quickly if needed. Also, in a display embodiment of the patterned target 300, the pattern 302 may not require illu mination from the light sou rces 110.

[00111] In an example, the patterned target 300 has a length LY' in the y-direction that is the same as the length LY of glass panel 10 (see FIG. 1A). Also in an example, the patterned ta rget 300 has a length (height) LZ' that is sufficient to appear to be reflected from the entirety of u pper su rface 12 of glass panel 10. In an example, length LZ' is at least 0.5 meters.

[00112] With reference again to FIGS. 10A, 10B and 11A, 11B, the patterned target 300 is arranged so that pattern 302 is reflected by the upper su rface 12 of the glass panel 10 and captured by the digital video camera 130, which in an example resides at a fixed height H relative to a horizontal reference l ine. In another example, height H is adjusta ble. As with the case of the cathode 220, the reflection angle Θ is relatively large (e.g., greater than 60 degrees or greater than 80 degrees) so that the reflectivity from the upper su rface 12 of the glass panel 10 is relatively high.

[00113] The pattern 302 of the patterned target 300 preferably has a pitch p chosen based on the resolution of the image sensor 133 in the digital video camera 130 and the expected amounts of deformation for the glass panel 10 such as caused by the lifting pins 44 of the susceptor 40.

[00114] In the operation of monitoring system 100 as configured in a reflection Moire mode, a reference or calibration digital image 132R such as discussed above is first captu red in a first exposu re wherein the patterned target 300 is ca ptured with a minimum of distortion. This can be accomplished for example by using a thick reference substrate or by having the glass panel 10 supported on the upper surface 42 of the platen 41. In an example, two different reference images 132 are employed: One at a "high" position on the susceptor 40 correspond ing to the position where the glass panel 10 is supported by the lifting pins 44, and one at a "low" position on the susceptor where the glass panel is supported on the u pper surface 42 of the platen 41. Also in an example, multiple different reference images based on different patterns 302 can also be employed.

[00115] Once the first exposu re is performed and at least one reference digital image 132R captured, then the lifting pins 44 can be actuated to lift the glass panel 10 off of the platen 41. Supporting the glass panel 10 by the lifting pins 44 allows gravity to deform the glass panel. Second exposu res are then performed to capture measurement digita l images 132M by the digital video camera 130 as the glass panel 10 deforms during lifting. In an example, the measu rement digital images 132M are captured at as high a rate as possible (e.g., 6 to 10 frames per second), and using as high an imaging resolution as possible (e.g., 24 megapixel digital single-reflex camera 130) to capture the details of the transient deformations by capturing a high-fidelity digital image of the Moire pattern. Multiple different measu rement digital images 132M can be captured based on the different patterns 302 presented by the patterned ta rget 300.

[00116] Once a desired nu mber of measu rement digital images 132M are captu red, then reflection Moi re image processing is carried out. This involves su perim posing the measurement digital images 132M and the corresponding reference d igital image 132R to create a set 400 of double-exposu res or interferograms 401, with each having a Moire pattern 402, such as shown in FIG. 13. Each interferogram 401 corresponds to a time t, and FIG. 13 shows times t = ti, ...tio, tn, tn, - The Moire pattern 402 for time t = n is based on an actual Moire pattern obtained du ring the time when the glass panel 10 was lifted by the lifting pins 44 as part of the remova l phase after plasma processing. The Moire pattern 402 comprises Moire fringes ("fringes") 404 that represent the slope or first derivative of the displacement of the upper surface 12 of the glass panel 10.

[00117] The Moire pattern 402 for t = t₁₂ includes a convergence of fringes 404 at a location L44 associated with one of the center six lifting pins 44. The maximu m cu rvature of the fringes 404 are locations of maximu m slope of the upper su rface 12 of the glass panel 10. It is noted that the captu re of digital images 132M allow for the time evolution of the Moire pattern to be observed and evaluated to determine how deformations such as locations of maximum bending stress change with time. This can include for exam ple, changes to the glass panel 10 cause by thermal gradients due to heating by a heated susceptor 40.

[00118] If dSS/dx and dSS/dy represent the (x,y) surface slope information for surface SS(x,y) of the upper su rface 12 of the glass panel 10, then determining the maximu m bending stresses σ in the glass requires calculating d²SS/dx² and d²SS/dy² (i.e., σ_χ ~ d²SS/dx² and Oy ~ d²SS/dy²). Qualitatively, the "zero" order fringes 44 determine the locations of minimu m bending curvatu re and therefore represents locations of maximu m bending stress in the glass panel 10₇ as indicated by the lifting-pin location L44 in FIG. 13. Thus, in an example, the characterization of the glass panel 10 can include determining amounts of stress and stress locations, as well as time-varying changes in the amount of stress and the location of the stress.

[00119] In an example, the above-described Moire process for characterizing the glass panel 10 is ca rried out for multiple different reference images 132R and corresponding multiple different measu rement images 132M.

[00120] It wil l be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosu re as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the a ppended claims and the equivalents thereto.

Claims

What is claimed is:

1. A method of cha racterizing a glass panel comprising the steps of:

a) performing a plasma-based treatment of an upper surface of the glass panel that resides proximate a cathode;

b) du ring the plasma-based treatment, capturing measu rement digital images of at least a portion of the glass panel, wherein the measurement digital images comprise a distorted reflection of the cathode from the upper surface of the glass panel due to a distorted surface shape of the upper surface of the glass pa nel;

c) estimating the distorted surface shape of the upper su rface of the glass panel as a function of the distorted reflection of the cathode; and

d) identifying at least one deformation of the glass panel using the estimated distorted surface shape of the upper surface of the glass panel.

2. The method accordi ng to claim 1, wherein at least a portion of the measurement digital image is captured at a reflection angle of greater than 60 degrees.

3. The method accordi ng to claim 1, wherein the plasma-based treatment ta kes place in a chamber having multiple windows, and wherein the capturing measurement digital images is performed by first and second digital video cameras having respective first and second viewing directions that are perpendicular to each other.

4. The method accordi ng to claim 3, wherein first and second light sources are arranged on either side of at least one of the digital video cameras and wherein the first and second light sources illuminate the glass panel through respective windows of the multiple windows.

5 The method according to claim 1, wherein the glass panel has a side with a length of at least 1 meter a nd a thickness of between 0.3 millimeters and 0.7 millimeters.

6. The method accordi ng to claim 1, wherein the plasma-based treatment ta kes place in an interior of a cha mber, and further comprises the presence of one or more reference featu res on at least one of the upper su rface of the glass panel and within the chamber interior.

7. The method accordi ng to claim 1, wherein estimating the distorted surface sha pe of the u pper su rface of the glass panel comprises:

i) making an initial estimate of the distorted surface shape and generating therefrom a simulated reflection of the cathode;

ii) determining a first amount of error between the simu lated reflection of the cathode and the distorted reflection of the cathode;

iii) generating a new estimate of the distorted su rface shape with a second amount of error; and

iv) repeating i) through iii) until the second amount of error becomes less than an error tolerance.

8. The method according to claim 7, wherein the digital image of the reflection of the cathode comprises a plura lity of line reflections of the cathode, and wherein the determining a first amount of error comprises determining a difference between a line reflection in a reference image and a corresponding line reflection in at least one of the measurement digital images.

9. The method according to claim 1, further comprising:

capturing a reference digital image of the portion of the glass panel, wherein the reference digital image includes a substantially u ndistorted reflection of the cathode; and performing a ca libration of the measu rement digital images using the reference digital image.

10. The method accordi ng to claim 1, wherein the plasma treatment comprises performing plasma-enhanced chemical vapor deposition.

11 The method accordi ng to claim 1, wherein the plasma treatment is performed in a chamber having a top section that includes the cathode, and further comprising:

removing the top section of the chamber;

operably disposing a patterned target relative to the upper su rface of the glass panel to create a reflection Moire geometry;

capturing a first digital image of the patterned target as reflected from the upper surface of the glass panel as the glass panel is supported by an upper su rface of a platen; capturing second digital images of the patterned target as reflected from the upper surface of the glass panel while lifting the glass panel off of the upper surface of the platen; superimposing the first digital image with the second digital images to form interferograms having a Moire pattern; and

examining the Moire pattern to identify at least one region of maximu m bending of the glass panel.

12. The method accordi ng to claim 11, wherein the interferograms show a time evolution of the su rface shape of the upper su rface of the glass panel du ring said lifting of the glass panel off of the upper su rface of the platen.

13. The method accordi ng to claim 1, wherein the measurement digital images are digital video images.

14. A method of characterizing deformations in a glass panel comprising the steps of: a) performing a plasma-based treatment of an upper surface of the glass panel that resides proximate a cathode;

b) generati ng a reference digital image of the glass panel that comprises a substantial ly undistorted reflection of the cathode;

c) during the plasma treatment, capturing measurement digital images of the glass panel that comprise a distorted reflection of the cathode due to a distorted su rface shape of the u pper su rface of the glass panel;

d) determining whether the upper su rface of the glass panel is distorted as a fu nction of a compa rison between the substantially undistorted reflection of the cathode of the reference digital image and the distorted reflection of cathode in the captured measurement digital images; and

e) identifying the at least one deformation of the glass panel as a function of the determination.

15. The method according to claim 14, wherein the digital image of the reflection of the cathode comprises a plura lity of line reflections of the cathode and wherein the reference digital image comprises reference lines, and wherein determining an amou nt of error comprises determining a difference between a reference line in the reference digital image and a corresponding line reflection in at least one of the measurement digital images.

16. The method accordi ng to claim 15, wherein the step d) comprises:

i) making an initial estimate of the distorted surface shape and generating therefrom a simulated reflection of the cathode that includes a simu lated line reflection;

ii) determining an amount of error between the simu lated line reflection and the corresponding line reflection of the at least one measurement digita l image;

iii) using the amount of error, making a new estimate of the distorted surface shape that reduces the amou nt of error; and

iv) repeating i) through iii) until in ii), the error is reduced to less than a select error tolerance.

17. The method according to claim 14, wherein at least a portion of the measurement digital image is captured at a reflection angle of greater than 60 degrees.

18. The method accordi ng to claim 14, wherein the plasma-based treatment takes place in a chamber having at least one window, and wherein captu ring the measurement digital images is performed by at least one digital video camera that views the glass panel through the at least one window.

19. The method according to claim 14, wherein the glass panel a side with a length of at least 1 meter a nd a thickness of between 0.3 millimeters and 0.7 mil limeters.

20. The method accordi ng to claim 14, wherein the plasma-based treatment takes place in an interior of a cha mber, and further comprises the presence of one or more reference featu res on at least one of the upper su rface of the glass panel and within the chamber interior.

21. The method accordi ng to claim 14, wherein the plasma treatment is performed in a chamber having a top section that includes the cathode, and further comprising:

removing the top section of the chamber;

capturing a first digital image of the patterned target as reflected from the upper surface of the glass panel as the glass panel is supported by an upper su rface of a platen; capturing second digital images of the patterned target as reflected while lifting the glass panel off of the upper surface of the platen;

superimposing the first digital image with the second digital images to form interferograms having a Moire pattern; and

examining the Moire pattern to identify at least one region of maximum bending of the glass panel.

22. The method accordi ng to claim 21 wherein the interferograms show a time evolution of the surface shape of the upper surface of the glass panel during said lifting the glass panel off of the upper surface of the platen.

23. The method accordi ng to claim 22, wherein the measu rement digita l images are digital video images.