Abstract:
The present invention discloses a new electron spectroscopic metrology system using an electron beam to measure the periodic feature on a substrate. The present invention provides a measurement system for the geometry parameters of the periodic feature which is only a few repeating small elements in the measurement area. The present invention has the following advantages: (1) capable of measuring a small feature of an array of lines (line width less than a couple of ten nanometers); (2) capable of measuring a small feature of an array of via holes; (3) capable of measuring an isolated feature, with a line and patch ratio less than 1:10; (4) capable of measuring a small area, less than twenty five square micrometers; (5) no need to input detailed knowledge about the feature and its film stack; (6) simple theoretical model to derive the geometry parameters. The total simplicity of the present invention will enhance the electron spectroscopic metrology system&#39;s overall performance and productivity.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     (1) Field of the Invention  
         [0002]     The present invention relates to the field of metrology monitoring and process controlling of wafer fabrication processes, especially the photolithography and etching processes.  
         [0003]     (2) Prior Art  
         [0004]     The general way to monitor the wafer fabrication processes is by using a critical dimension scan electron microscope (CDSEM). The CDSEM generates an image from the electron intensity profile of the line-scan of the probe electron beam at the viewing area. Different topography and materials will have different electron deflection and second electron yields. The detector collects all the electrons available from the specimen during the line-scan, pixel by pixel, regardless of the energies of these electrons. The CD measurement can be taken either on the apparent feature on the image constructed from the line scanning or on the line scan itself The major limitations for the CDSEM are the less geometric resolution due to the large interaction volume, the low contrast, and most of the time, edge glowing and/or blurring. To reduce the limitations due to the large interaction volume and edge glowing, the acceleration energy of the probing electron beam is drastically reduced. Different coating techniques have been explored to enhance the contrast for current available materials, which either have the small atomic number, Z, for low −k dielectric materials or close atomic numbers for adjacent layers, such as a thin layer of silicon nitride or silicon oxide with polycrystalline silicon. People have been working on techniques to improve the CDSEM measurement, for example Tanaka et al in U.S. Pat. No. 6,706,543. Houge et al also proposed the multiple parameter characterization (MPC) algorithms to improve the CDSEM measurement mathematically in U.S. Pat. No. 6,714,892. But the nature of the CDSEM based metrology remains the same and its basic limitations are still a hurdle for metrology measurements requiring high precision and better repeatability.  
         [0005]     In recent years, optical CD measurement tools, such as Spectroscopic CD (SCD) or Optical Profilometry (OP) have been developed as alternatives for the CD measurement. The optical spectroscopic CD techniques are mainly based on the UV-Vis light interference of the grating like feature on a substrate. The optical CD techniques measure the reflection and/or the phase changes between different polarizations of light as a function of the wavelength or the angle that is between the incident light and the detected light. There are mainly three different types of optical CD tools: (1) varying incident angle profilometry, angle-resolved scatterometer by Acct Optical Technologies Inc partially in U.S. Pat. No. 6,606,152; (2) spectroscopic ellipsometer by KLA-Tencor Technologies Corp. in U.S. Pat. No. 6,590,656 and Timbre Technologies Inc. in U.S. Pat. No. 6,645,824, and (3) the spectroscopic profilometry by Novo Measuring Instruments Ltd. in U.S. Pat. No. 6,704,920. The light source for the optical CD tools are in the range of UV-Vis (190 nm to 800 nm) and the angle-resolved scatterometer uses a single wavelength laser in UV-Vis range. As the size of the semiconductor devices continues to decrease to 25 nm, the interference from UV-Vis optical scatterometer losses its sensitivity drastically. The UV-Vis light scatterometer applications are limited to an array of dense lines only, not for via holes or trenches, due to its limited resolution power. The other fundamental limitations of the UV-Vis light scatterometer are that a) it requires a relatively large area (2500 square micrometers); b) a special manufactured periodic feature on the substrate for the measurement; and c) detail knowledge of the feature and associated film structures.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     In primary aspect, the present invention discloses a new type of electron spectroscope metrology system that uses an electron spectroscopic scattering technique to measure a periodic feature on a substrate during IC fabrication processes, such as lithography and etch processes. The electron spectroscope metrology system of the present invention is an energy-resolved metrology system, which provides a method to perform the diffraction measurement with an electron beam having a wavelength much shorter than the size of the periodic feature on the substrate. The electron spectroscopic scattering technique collects the electron intensity over a range of wavelength and yields the information of the periodic feature only from the very top surface of the feature due to electron nanometer level escaping depth. The present invention further derives the geometry parameters from said electron spectroscopic scattering spectra. The geometry parameters of the periodic feature include, a) the pitch that is the sum of the width of the repeating element; b) the critical dimensions (CD) that is the line width of the element at certain z height; and c) the side wall angle of the line.  
         [0007]     Because of its nature of using an electron beam and doing the electron scattering spectroscopy, the present invention has the following advantages. 
        a) The present invention provides the necessary sensitivity and control-ability to measure a small area of several square micrometers.     b) The present invention provides said measurement for small size of the periodic feature, for an array of lines, the line width being equal or less than a couple of ten nanometers.     c) The present invention provides the measurement for small size of the periodic feature, for an array of via holes or of trenches.     d) The present invention provides the measurement for small size of the periodic feature, for an array of via holes or of trenches.     e) The present invention provides the measurement for a fewer feature in the measurement area, isolated feature.     f) The present invention produces the chemical elemental information during said measurement, opposite to the optical scatterometer techniques that require the detail knowledge about the feature and materials prior to a measurement, provides the chemical elemental information of the periodic feature or film.        
 
         [0014]     In another aspect, the present invention provides the apparatus of the electron spectroscope metrology system that measures a periodic feature on a substrate during IC fabrication processes. Said apparatus includes: 
        a) an electron source which emits the electron beam at a selected energy within a range of beam energies;     b) a means of electron detection which collects the reflection and diffraction electrons from the periodic feature to build a scan electron microscope image.     c) a means of electron spectroscopic analyzer which collects the diffracting electrons from said periodic feature over an energy range. The angle between the electron beam and the electron spectroscopic analyzer is fixed.     d) an algorithm to calculate the geometry parameters by comparing the measurement spectrum to the theoretical models.     e) a stage to hold and move the substrate during said measurement process; a means of stage and substrate alignment such as pattern recognition device which aligns the measurement feature and the substrate to pre-selected periodic feature;     f) a vacuum chamber to keep the substrate, electron source, electron detection and analyzer devices, and stage under vacuum.        
 
         [0021]     In further aspect, the present invention discloses a new type of electron spectroscope metrology system that uses an electron spectroscopic scattering spectrum with angle-resolved technique to measure a periodic feature on a substrate during IC fabrication processes. Said angle-resolved electron spectroscopic scattering spectroscopy collects the electron intensity over a range of angle that is defined as the angle between the electron beam and the detection beam of the electron spectroscopic analyzer and it yields similar information regarding the feature geometry as said energy-resolved electron spectroscopic scattering spectroscopy. Said angle-resolved electron spectroscopic scattering spectroscopy in the present invention further derives the geometry parameters using a theoretical model different from said energy-resolved electron spectroscopic scattering spectroscopy.  
         [0022]     Said angle-resolved electron spectroscopic scattering spectroscopy of the present invention has similar advantages as said energy-resolved electron spectroscopic scattering spectroscopy.  
         [0023]     In another aspect, the present invention provides the apparatus of said angle-resolved electron spectroscope metrology system, including different means than said energy-resolved electron spectroscope metrology system: 
        a) an electron source which emits the electron beam at a selected energy;     b) a means of the electron spectroscopic analyzer which collects the diffracting electrons from said periodic feature over a range of angles.     c) a means of varying the angle between said electron beam and the electron spectroscopic analyzer.     d) an algorithm to calculate the geometry parameters by comparing the measurement spectrum to the theoretical models.        
 
         [0028]     In further aspect, the present invention discloses a new type of electron spectroscope metrology system that uses an electron spectroscopic scattering spectrum with both energy-resolved and angle-resolved technique to measure a periodic feature on a substrate. Said energy-resolved and angle-resolved electron spectroscopic scattering spectroscopy collects the electron intensity over a range of energy and over a range of angle separately. Said energy-resolved and angle-resolved electron spectroscopic scattering spectroscopy in the present invention further derives the geometry parameters using a theoretical model combining both said energy-resolved and said angle-resolved electron spectroscopic scattering spectroscopes.  
         [0029]     In another aspect, the present invention provides the apparatus of said energy-resolved and angle-resolved electron spectroscope metrology system, comprising: 
        a) an electron source which emits the electron beam at a selected energy;     b) a means of the electron spectroscopic analyzer which collects the diffracting electrons from said periodic feature over an energy range.     c) a means of varying the angle between said electron beam and the electron spectroscopic analyzer.        
 
         [0033]     In an additional aspect, the present invention provides additional means for loading and unloading said substrate and substrate pr-alignment, including the cassette stations; the loading and unloading mechanism; the substrate pre-alignment device.  
         [0034]     Further objects and advantages of the present invention will become apparent from a consideration of the following description and drawings.  
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF DRAWINGS  
       [0035]     The novel features believed characteristic of the present invention are set forth in the claims. The invention itself, as well as other features and advantages thereof will be best understood by referring to detailed descriptions that follow and when read in conjunction with the accompanying drawings.  
         [0036]     Reference is specifically made to the drawings wherein like numbers are used to designate like members throughout.  
         [0037]      FIG. 1   a  is a schematic drawing of a UV-Vis spectroscopic scatterometer of prior art.  
         [0038]      FIG. 1   b  is a schematic drawing of a varying angle UV-Vis scatterometer of prior art.  
         [0039]      FIG. 2   a - 2   d  show the embodiments of the cross section view and the top down view of the periodic feature of the present invention.  
         [0040]      FIG. 2   a  is a cross sectional view of the periodic feature of an array of lines on a substrate.  
         [0041]      FIG. 2   b  is a top down view of the periodic feature shown in  FIG. 2   a.    
         [0042]      FIG. 2   c  is a top down view of the periodic feature of an array of via holes on a substrate.  
         [0043]      FIG. 2   d  is a top down view of the periodic feature of an array of trench on a substrate.  
         [0044]      FIG. 3  is a schematic of the preferred electron spectroscopic metrology system having the electron beam from the electron source with a SEM electron detector, and an electron spectroscopic analyzer aligned, combined with a substrate loading and unloading system of the present invention.  
         [0045]      FIG. 4  is a schematic of the preferred electron spectroscopic metrology system with an electron spectroscopic analyzer separated from the electron source, combined with the substrate loading and unloading system.  
         [0046]      FIG. 5   a - 5   c  are graphical representations of the electron spectroscopic scattering spectrum for periodic feature of an array of lines by the preferred electron spectroscopic metrology system of the present invention. The measurement spectra are taken with the incident angle of the electron beam perpendicular to said feature.  
         [0047]      FIG. 5   a  is a graphical representation of the electron spectroscopic scattering spectrum for an array of dense lines on a substrate by the preferred electron spectroscopic metrology system of the present invention. The measurement is assumed with the electron beam perpendicular to said array of isolated lines.  
         [0048]      FIG. 5   b  is graphical representation of the electron spectroscopic scattering spectrum on an array of dense lines on a substrate by the preferred electron spectroscopic metrology system of the present invention. The measurement is taken with the electron beam parallel to said array of dense lines.  
         [0049]      FIG. 5   c  is graphical representation of the electron spectroscopic scattering spectrum on an array of isolated lines on a substrate by the preferred electron spectroscopic metrology system of the present invention. The measurement is assumed with the electron beam perpendicular to said array of isolated lines. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0050]     While preferred embodiments of the present invention will be described below, those skilled in the art will recognize that other hardware configurations including the electron beam from said electron source, the scan electron microscope (SEM) electron detector, the electron spectroscopic analyzer, the stage, and the substrate loading and unloading system, are capable of implementing the principles of the present invention. Thus the following description is illustrative only and not limiting.  
         [0051]     Reference is specifically made to the drawings wherein like numbers are used to designate like members throughout.  
         [0052]     Note the followings: 
        (1) The dimensions of all of drawings are not to scale.     (2) The normal direction of the sample is equivalent to the oblique angle of zero degree.     (3) The capabilities of the scan electron microscope image and pattern searching and substrate alignment of the present invention are available for all the configurations in drawings  FIG. 3  and  FIG. 4 .     (4) The electron spectroscopic analyzer in the different configurations,  FIG. 3  and  FIG. 4 , of the present invention can be the same or different.     (5) The substrate, the film stack, and the periodic feature in drawings  FIG. 3  and  FIG. 4  are used as the same to illustrate the principle and functionality of the present invention.     (6) The substrate may be of either silicon or germanium or other materials.     (7) The array of lines as embodiments of the present invention is illustrated in  FIG. 2 . However said electron spectroscopic metrology system measurement is applicable to other type of periodic patterns, such as an array of contact via holes.     (8) The array with non-flat topography feature as embodiments of the present invention is illustrated in the  FIG. 2  and  FIG. 4 . However the present invention is applicable to the flat topography features that have periodic patterns made by different material.     (9) The stage, the robot, the cassette station, and the cassette in the drawing  FIG. 3  and  FIG. 4  can be the same or different for each configuration and system.        
 
         [0062]      FIG. 1   a  is a cross sectional view of prior art of the UV-Vis optical scatterometer. The UV-Vis optical scatterometer with many variations is the main technique nowadays for optical CD measurement. The stage  150  moves the substrate to a certain location precisely so that the UV-Vis light  110  will illuminate on the pre selected pattern on the surface of said substrate  140 . Normally the UV-Vis light sources have the wavelength range of 180 nm to 780 nm. The spectroscopic ellipsometer photon detector  130  detects the light from the periodic feature and generates the ellipsometry spectra. The photon detector  120  detects the reflection intensity of the light and the resulted reflectometer spectrum can be used to produce the film information, the thickness of the film (s) on the substrate surface and optical index. The geometry information of the periodic feature can be generated from the ellipsometry spectra with the additional film information from said reflectometer spectrum.  
         [0063]      FIG. 1   b  is a cross sectional view of a prior art of typical varying angle scatterometer. A varying angle scatterometer uses either a single wavelength light source  110  or a multiple wavelength light sources, not shown. A reflection detector  120  detects the reflection intensity as the angle  160  sequentially varies over a range, which results in the angle-resolved scattering spectrum. The parameters of the periodic feature can be calculated from said angle-resolved scattering spectrum. The stage  150  moves the substrate  140  to a measurement area precisely for measurement. Like the other types of optical CD techniques, the varying angle scatterometer technique requires the inputs of film thickness and optical index in order to calculate the geometry parameters.  
         [0064]      FIGS. 2   a  and  2   b  are the cross sectional view and top down view of a periodic feature  270  on substrate  290  respectively, which will be used as embodiment in the present invention. There are three CDs, the top CD  210 , the middle CD  220 , the bottom CD  230 , the side wall angle  240  and the feature height  250 . The pitch  260  and the CD (s) define the periodic property of said periodic feature. The periodic feature  270  may be made of a film stack with different materials and different thickness. The side wall angle  240  and the height  250  of the feature are important for determining the overall cross section profile. There may be film (s)  280  between substrate  290  and periodic feature  270 . Unlike the other techniques in the prior arts, the electron spectroscopic metrology system of the present invention does not require film information for neither  270  nor  280  for deriving the parameters of the periodic feature.  
         [0065]      FIG. 2   c  is a top down view of the array of via holes with diameter  211  and pitch  261  that can be measured by the electron spectroscopic metrology system of the present invention.  
         [0066]      FIG. 2   d  is a top down view of the array of trenches with CD  212  and pitch  262  that can be measured by the electron spectroscopic metrology system of the present invention.  
         [0067]      FIG. 3  is a cross section view of the embodiment of the present invention. The electron spectroscopic metrology system  390  of the present invention operates under vacuum. The electron source, the scan electron microscope (SEM) electron detector, and the electron spectroscopic analyzer are assembled together as part of  310 . The electron source produces an electron beam at certain energy level ranging from 1 kV to 20 kV and at a certain angle  380  relative to the periodic feature. The electron beam excites a large amount of Auger electrons and scattered electrons from the periodic feature  270 . The SEM electron detector  310  collects the second electrons and generates SEM image. The electron spectroscopic analyzer  310  detects the scattered electrons and the Auger electrons simultaneously. The incident angle  380  of said electron beam from said electron source and the electron spectroscopic analyzer  310  is fixed to a predetermined angle in order to maxim the emitted electrons.  
         [0068]     The embodiment of the electron spectroscopic metrology system  390  in the present invention uses energy scan with a fixed angle, φ 0 , between the incident beam and the periodic feature  270 . The angle, φ 0 , is selected for the maxim scattering electrons and minimum background. Then, the scattered electron intensity vs. the emitted electron energy, E, is recorded as the energy-resolved spectroscopic scattering spectrum, I(E, φ 0 ).  
         [0069]     The wavelength of the electron beam is significantly shorter than the feature size, less than one nanometer vs. tens of nanometers, respectively. Shorter wavelength of the probing electron beam will simplify the theoretic model used to derive the geometry parameters of the periodic feature from the electron spectroscopic scattering spectrum. The nature of the high lateral resolution of electron beam technique enables the embodiment of the present invention to precisely define a much smaller measurement area with fewer and smaller periodic features compared to the UV-Vis optical scatterometer techniques.  
         [0070]     The embodiment of the present invention applies its image processing capability to navigate the stage  330  to a pre defined measurement area and to identify the measurement pattern, such as  270 . Then the stage  330  carries substrate  320  to the precise position and aligns the feature  270  exactly for future scattering measurement.  
         [0071]     The embodiment of said electron spectroscopic metrology system  390  in the present invention combining with a substrate loading and unloading device  340 , which includes a substrate cassette  350 , a robot  370 , and a cassette station  360 . The robot  370  transfers the substrate(s)  320  between the cassette  350  and the stage  330 .  
         [0072]     There may have a substrate pre-aligner in the electron spectroscopic metrology system  390 , which aligns the substrate to a precise orientation before said substrate being transferred into the electron spectroscopic metrology system  390 . The robot  370  will transfer the substrate(s)  320  between the cassette  350  and the pre-aligner and said stage  330 . Said substrate pre-aligner is not shown in both  FIG. 3  and  FIG. 4 .  
         [0073]      FIG. 4  is a cross section view of the embodiment of the present invention. The electron spectroscopic metrology system  490  of the present invention operates under vacuum. The electron beam from the electron source and second electron detector  410  is separated from the spectroscopic electron spectroscopic analyzer  411 . There are two major versions of configurations of the present invention, the single energy angle-resolved type, I(E 0 , φ) and the multi energy angle-resolved type, I(E I , φ). 
        A) Said single energy angle-resolved type uses a fixed collection energy, E 0 , for the analyzer  411  and collects the electron intensity vs. said angle  480 , φ, that varies over a certain angle range.     B) Said multiple energy angle-resolved type collects the electron intensity against the energy, E I , and said angle  480 , φ, which generates a 3-dimensional spectrum, I(E I , φ).          
         [0076]     The interpretation of the electron spectroscopic scattering spectrum and the calculation of the geometry for the periodic feature will be different for the two types of configurations.  
         [0077]     The electron source produces an electron beam in the energy range of 1 kV to 20 kV, which excites a large amount of scattered electrons and Auger electrons from the periodic feature  270 . The electron spectroscopic analyzer  411  detects said scattered electrons and said Auger electrons over a collecting energy range. The embodiment of the present invention has image processing capability to navigate the stage  430  and to align the substrate  420  to the precise position for the scattering measurement.  
         [0078]     The electron spectroscopic metrology system  490  in the present invention has a substrate loading and unloading device  440  and a robot  470 . The robot  470  transfers the substrate(s)  420  between the cassette  450  and the stage  430 . A substrate pre-aligner may also be used in the electron spectroscopic metrology system  390 , which aligns the substrate to a precise orientation before loading said substrate into the electron spectroscopic metrology system  390 . Then, the robot  370  will transfer the substrate(s)  320  between the cassette  350  and said pre-aligner and the stage  330 .  
         [0079]     The selection of configuration of the present invention depends on the specific requirements for the given applications.  
         [0080]      FIG. 5   a  is the graphical drawing of the electron spectroscopic scattering spectrum  510  generated by the energy-resolved electron spectroscopic metrology system of the present invention. The electron scattering spectrum  510  is generated with the incident electron beam perpendicular to the lines in the array of dense lines, the line to patch ratio of 1:2. There are Auger electron peaks  520  and  530  that are characteristic to certain chemical elements and the ratio of the peaks proportional to the material&#39;s atomic composition. The scattered electrons are slowly changing and featureless. The zoom-in spectrum  540  shows the diffraction interference due to the geometry of the array of dense lines. The geometry parameters of said lines can be obtained from the diffraction interference by using the preferred software system in the present invention.  
         [0081]      FIG. 5   b  is the graphical drawing of the electron spectroscopic scattering spectrum  550  generated by the energy-resolved electron spectroscopic metrology system of the present invention. The spectrum  550  is generated for said array of dense lines as in  FIG. 5   a , but the incident electron beam parallel to the lines of said array of dense lines. The Auger peaks  520  and  530  remains the same as in  FIG. 5   a . The zoom-in spectrum  560  shows no diffraction interference because of the relative orientation of said incident electron beam to said lines of the array. The spectrum  550  will be used as the background for the scatterometer measurement. To simplify the calculation of the geometry of the periodic feature, the background spectrum  550  can be subtracted from the spectrum  510 .  
         [0082]      FIG. 5   c  is the graphical drawing of the electron spectroscopic scattering spectrum  570  generated by the energy-resolved electron spectroscopic metrology system of the present invention. The electron scattering spectrum  570  is generated with the incident electron beam perpendicular to the lines of the array of the isolated lines, the line to patch ratio of 1:10. The extreme short escape length of the electrons gives the embodiment of the present invention sufficient surface sensitivity to measure only a few lines of the array of isolated lines compared to a few tens of lines required by the UV-Vis optical scatterometer technologies. The Auger electron peaks  520  and  530  remains the same as that in  FIGS. 5   a  and  5   b , because of the identical film stack of the feature and neglecting the shadow effect. The zoom-in spectrum  580  shows a different diffraction interference due to the change of the line density.  
         [0083]     Although the description above contains specifications, these should not be construed as limiting the scope of the present invention but as merely providing illustrations of some of the presently preferred embodiments of the present invention. Therefore the scope of the present invention should be determined by the claims and their legal equivalents, rather than by the examples given.  
         [0000]     Claims: