Abstract:
An apparatus for inspecting a wafer, comprising a first illuminator for radiating an illumination beam in a first illumination beam path onto a surface of the wafer and being configured as continuous light source; a second illuminator for radiating an illumination light beam in a second illumination beam path onto a surface of the wafer and being configured as continuous light source; a first detector means defining a first detection beam path; a second detector means defining a second detection beam path, wherein the first and the second detector means have a predetermined spectral sensitivity and detect data of at least an illuminated area moveable in a scanning direction on the surface of the wafer in a plurality of different spectral ranges.

Description:
[0001]    This claims the benefit of German Patent Application No. DE 10 2006 059 190.9, filed on Dec. 15, 2006 and hereby incorporated by reference herein. 
         [0002]    The present invention relates to an apparatus for inspecting a wafer, including a first illumination device for radiating an illumination light beam in an illuminating beam path onto a surface of the wafer, and a second illumination device for radiating an illumination light beam in a second illumination beam path onto the surface of the wafer. A first detector is also provided, which defines the first detection beam path. In addition, a second detector is provided, which defines a second detection beam path. The two detectors have a predetermined spectral sensitivity, and the data from an illuminated area on the surface of the wafer is detected in a plurality of different spectral ranges. 
       BACKGROUND 
       [0003]    To improve quality and efficiency in the manufacture of integrated circuits, apparatus for detecting macro defects on the surface of wafers are used, so that wafers found to be defective can be rejected or post-processed until the quality of a currently inspected wafer is sufficient. 
         [0004]    Optical inspection apparatus are known, which radiate an illumination light beam by means of an illumination device onto a surface of the wafer. An image recording means is also provided to detect an image or data from the illuminated area on the surface of the wafer in a plurality of spectral ranges, i.e. spectrally resolved. Herein, there can be problems with the further processing of the color signals detected by the image detector if the color image channels of the image detector are driven in an irregular fashion, which can result in relatively low signal to noise ratio or to overdriving in the individual color signals. 
         [0005]    German patent application publication DE 101 32 360 discloses an apparatus for the color neutral brightness adjustment in the illumination beam path of a microscope. The invention is based on the idea that with microscopes operated with an incandescent lamp similar to a black light, the color temperature of the color spectrum emitted by the incandescent lamp is shifted from the blue spectral range to the red spectral range when the input lamp power is reduced. To compensate the red shift a variable optical filter is provided in the illumination beam path having a variable transmission for red light across the filter area. By displacing the filter in the illumination beam path, a blue shift is caused, which is compensated by the red shift caused by the reduction of the electric power. 
         [0006]    German patent application publication DE 100 31 303 discloses an illumination apparatus having LEDs. Due to the degradation of the LED material, the intensity and wave length of the light emitted by the LED changes over time. In order to achieve uniform illuminating characteristics, a feedback control is provided so that a predetermined color temperature and intensity of the LEDs can be maintained. 
         [0007]    U.S. Pat. No. 6,847,443 B1 discloses a system and a method for detecting surface defects by means of light that has a plurality of wavelengths with narrow band widths. The defects primarily occur in surface structures formed on the surface of a semiconductor wafer. A light source, preferably a flash lamp light source, is provided, which supplies the illumination light. The illumination light is divided into a plurality of selected bands having respective bandwidths by means of a filter. The light is then transferred to a diffuser by means of an optical fiber, and from there the light is directed onto the surface of a semiconductor wafer. A camera receives a plurality of images, wherein each image has been produced from a different section of the spectrum. The images can be generated both by reflected and diffracted light. The images can be stored or compared with the image of a calibration wafer. The small bandwidth of the illumination light is chosen such that the wavelength of the illumination light is in the range of maximum sensitivity of each camera channel. By comparing the measured light intensities with the light intensities measured on a defect free wafer, the contrast values can be determined for each area of the wafer surface. It has been shown that the larger the defect, the greater the contrast value. The narrow band illumination and the associated narrow band detection result in the contrast being substantially improved. However, this principle is not sufficient to further improve the detection speed and the detection sensitivity. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is to provide an apparatus, with which the detection speed and the detection sensitivity can be further improved. 
         [0009]    The present invention also provides an apparatus having a first illumination device for radiating an illumination beam in a first illumination beam path onto a surface of the wafer and being configured as continuous light source. A second illumination device is provided for radiating an illumination light beam in a second illumination beam path onto a surface of the wafer and being configured as continuous light source. A first detector defines a first detection beam path. A second detector defines a second detection beam path, wherein the first and the second detector have a predetermined spectral sensitivity and detect data of at least an illuminated area moveable in a scanning direction on the surface of the wafer. The detection is done in a plurality of different spectral ranges. 
         [0010]    According to another embodiment of the present invention, the above object is also achieved by an apparatus including only two illumination devices, each configured as a continuous light source. In addition, a polarizer may be provided in the illumination beam path of at least one of the illumination beam paths of the two illumination devices. 
         [0011]    The illumination device can include a light source which emits light having a plurality of discretely formed intensity peaks at different wavelengths. Moreover, the illumination device may include a continuously adjustable light source so that each required wavelength range can be set. It goes without saying that the spectral width of the wavelength range required can be adapted to the requirements needed for the inspection. 
         [0012]    The illumination device can further include an LED illumination. The illumination device can also be provided as a broad band light source, wherein the individual wavelengths or wavelength ranges, are adjustable by means of corresponding filters. 
         [0013]    The detector can be configured as a line camera. It is also conceivable that the detector includes a trilinear detector, wherein the individual lines of the trilinear detector are each provided with a suitable wavelength filter. Moreover, the detector can include three light-sensitive chips arranged around a prism arrangement in such a way, that each of the chips receives a different wavelength. The detector may also include a two-dimensional light-sensitive chip having a dispersive element upstream of it which directs the different wavelength ranges onto different areas of the light-sensitive chip. This detector can be regarded as an imaging spectrometer. 
         [0014]    According to an embodiment of the present invention, a beam splitter is provided for making the light of the illumination device collinear with the detection beam path of the detector. The beam splitter used here can include polarizing characteristics. 
         [0015]    In another embodiment of the present invention, a first and a second illumination device, and a first and a second detector are provided. The illumination devices each include a continuous light source, and in the illumination beam path of at least one of the illumination devices, a polarizer may be provided in a further embodiment. 
         [0016]    The two illumination devices are arranged such that the light from the first illumination device and the second illumination device coincide in the same area on the surface of the wafer. The illumination beam path of the first illumination device is made co-linear with the detection beam path of the first detector via a beam splitter. 
         [0017]    The second illumination device and the second detector are arranged at an angle to the normal on the surface of the wafer. Herein, the angle at which the second detection beam path is inclined, is adjustable. 
         [0018]    The first detector can be configured to be monochromatic, for example, so that the detection has high resolution. The second detector can be polychromatic, for example, and has a lower resolution than the first detector. 
         [0019]    It is advantageous if a polarizer is arranged in at least one of the illumination beam paths. In addition, with grating-type structures (so-called zero order gratings) the orientation of the grating relative to the polarization direction can be determined. It is also possible to determine in this way whether or not (and if necessary where) there are grating structures on the wafer. This cannot be achieved with the usual rather low resolution in the range of &gt;5 μm in current macro inspection. If the grating period of the structures present on the wafer is in the area of a few illumination wavelengths and less, use of the present invention is particularly advantageous. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a schematic view of a system for detecting defects on wafers, or structured semiconductor substrates; 
           [0021]      FIG. 2   a  is a schematic representation of an embodiment of the present invention, wherein a first and second illumination device, and a first and a second detector are provided; 
           [0022]      FIG. 2   b  shows a possible arrangement of the illumination fields on the surface of the wafer; 
           [0023]      FIG. 3  is a schematic representation of a further embodiment of the present invention, wherein the illumination device and the detector are arranged at an angle to each other; 
           [0024]      FIG. 4  is a schematic representation showing how the whole surface area of a wafer, or a structured semiconductor component, is detected with the apparatus according to the present invention; 
           [0025]      FIG. 5   a  shows a detailed view of the arrangement shown in  FIG. 5   a , wherein the detector includes a trilinear detector; 
           [0026]      FIG. 5   b  shows another embodiment of the detector, wherein the detector includes a plurality of detector chips; 
           [0027]      FIG. 5   c  shows an embodiment of the detector, wherein the detector includes a two dimensional detector chip; 
           [0028]      FIG. 6   a  is a schematic representation of an embodiment of the arrangement of the illumination device and the detector, wherein a DMD is arranged in the illumination beam path; 
           [0029]      FIG. 6   b  is a schematic representation of a possible illumination pattern created by means of the DMD on the surface of the wafer; 
           [0030]      FIG. 7  is a representation of the light emitted by a line light source; 
           [0031]      FIG. 8  is a representation of the intensity characteristic of a continuously adjustable light source; 
           [0032]      FIG. 9  is a representation of the intensity characteristic of the light emitted by an LED; 
           [0033]      FIG. 10  is a schematic representation of the acquisition of corresponding spectral illumination bands, wherein the light source used is a broad band light source. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 1  shows a system for inspecting structures on semiconductor substrates. System  1  includes the present invention in its interior. System  1  consists, for example, of at least one cartridge element  3  for the semiconductor substrates or wafers. Images, image data or data of the individual wafers or structured semiconductor substrates are recorded in a measuring unit  5 . A transfer mechanism  9  is provided between cartridge element  3  for the semiconductor substrates or wafers and measuring unit  5 . The system itself is enclosed in a housing  11 , wherein housing  11  defines a base area  12 . Further, at least one computer is integrated in system  1 , which is for evaluating or processing the individual image data. System  1  is provided with a display  13  and a keyboard  14 . The user can make data inputs for controlling the system or even parameter inputs for evaluating the recorded data, image data or images from the individual wafers, using keyboard  14 . A plurality of user interfaces is shown to the user of system  1  on display  13 . In addition, information on the current measurement is shown to the user on the user interface. System  1  can further have a modular structure so that further measuring means (not shown) can be added to system  1 . The further measuring means are then usable for different inspection methods. 
         [0035]      FIG. 2   a  shows a further embodiment of the apparatus according to the present invention. Here, a first illumination device  20   1  is provided defining a first illumination beam path  20   a   1 . Further, a second illumination device  20   2  is provided defining a second illumination beam path  20   a   2 . The first illumination device  20   1  has a first detector  21   1  associated with it. Second illumination device  20   2  has a second detector  21   2  associated with it. In first illumination beam path  20   a   1  of first illumination device  20   1 , a beam splitter  25  is also provided for making first illumination beam path  20   a   1  collinear with first detection beam path  21   a   1 . Preferably beam splitter  25  is configured as a polarizing beam splitter. Second illumination beam path  20   a   2  of second illumination device  20   2  and second detector  21   2  are arranged in such a way that second illumination beam path  20   a   2  and second detection beam path  21   a   2  are inclined with respect to normal  30  on surface  22  of wafer  23  by a first angle  41  and a second angle  42 . First detector  21   1  and second detector  21   2  can be configured to be monochromatic or polychromatic. For the case in which detectors  21   1  or  21   2  are monochromatic, a high resolution detection of surface  22  of wafer  23  is possible. For the case in which detectors  21   1  or  21   2  are polychromatic, a low resolution detection of surface  22  of wafer  23  is possible. First angle  41 , which defines the inclination of second illumination beam path  20   a   2  with respect to normal  30 , is equal to second angle  42  at which second detection beam path  21   a   2  is inclined with respect to normal  30 , identifying it as a bright-field arrangement. A dark-field arrangement is also conceivable, wherein first angle  41  and second angle  42  are not equal. There is a plurality of embodiments for configuring detectors  21   1  or  21   2 . In second detection beam path  21   a   2 , a dispersive element is further arranged for directing light reflected from surface  22  of wafer  23  onto respective detector elements of the polychromatic detector.  FIGS. 8   a ,  8   b  and  8   c  show three different embodiments for the possible configuration of detectors  21   1  and  21   2 . 
         [0036]      FIG. 2   b  shows a possible arrangement of illumination fields  35   a  and  35   b  on surface  22  of wafer  23 . Apart from the possibility that illumination fields  35   a  and  35   b  of first illumination device  20   1  and second illumination device  20   2  are superimposed (not shown),  FIG. 2   b  shows illumination fields  35   a  and  35   b  separate from each other in scan direction  63 . Since wafer  23  is arranged on support means  28 , moveable in the x and y coordinate directions, illumination fields  35   a  and  35   b  move over dies  64  arranged on surface  22  of wafer  23 . 
         [0037]      FIG. 3  again illustrates the variable arrangement of illumination device  20  and detector  21 . In the arrangement shown in  FIG. 3 , illumination beam path  20   a  is inclined with respect to detection beam path  21   a  by an angle  41  or an angle  42  with respect to normal  30  on the surface of wafer  23 . If angle  41  is equal to angle  42 , this is referred to as a bright-field arrangement. If angle  41  is not equal to angle  42 , this is referred to as a dark-field arrangement. This has the particular advantage that the user can switch between the two arrangements according to his measuring problem. In one case, the bright-field arrangement may be better suited for solving a measuring problem than the dark-field arrangement, and vice versa. 
         [0038]      FIG. 4  shows how the detection or scanning of the entire surface  22  of a wafer  23  is carried out. The at least one illumination device  20  creates an illumination spot  60  on surface  22  of wafer  23 , corresponding to one of illumination fields  35   a  or  35   b  of  FIG. 2   b , when only one illumination device is provided. Illumination spot  60  can also result from overlapping two or more illumination fields from a plurality of illumination devices. Illumination spot  60  can be configured as a line, a small area, an area of any particular shape, or as a symmetric area. If the illumination spot  60  is a line, the length of illumination spot  60  is greater than its width. Illumination spot  60  is guided along a meandering line  61 , by moving wafer  23  in the x direction (scanning direction  63 , see arrow) and the y direction, in order to scan the entire surface  22  of wafer  23 . 
         [0039]      FIG. 5   a  is a detail view of the arrangement of  FIG. 2   a , wherein the detector includes a trilinear detector. Detectors  21   1  or  21   2  includes three detector lines  50   1 ,  50   2  and  50   3 , each of which is provided with a corresponding color filter  51   1 ,  51   2  and  51   3 . Using the trilinear detector, it is therefore possible for each of the detector lines  50   1 ,  50   2  and  50   3  to detect the light information from surface  22  of wafer  23  in a different color, depending on the embodiment of color filters or wavelength filters  51   1 ,  51   2  and  51   3 . 
         [0040]      FIG. 5   b  shows another embodiment of detector  21   1  and/or  21   2 , wherein the detector includes a plurality of detector chips  53   1 ,  53   2  and  53   3 . Detector chips  53   1 ,  53   2  and  53   3  are arranged around a dispersive arrangement  54 , for spectrally splitting the impinging light, so that the individual detector chips  53   1 ,  53   2  and  53   3  each receive different color information. In a particular embodiment, first detector chip  53   1  can detect red light, second detector chip  53   2  can detect green light and third detector chip  53   3  can detect blue light. 
         [0041]      FIG. 5   c  shows an embodiment of detector  21   1  and/or  21   2 , wherein the detector includes a two-dimensional detector chip  55 . In the present case, a dispersive element  70  is arranged in second detection beam path  21   a   1  or  21   a   2 . Dispersive element  70  is for spatially separating the spectral portions of the detected light in detection beam path  21   a   1  or  21   a   2 , so that the detected light can be imaged onto the individual detector lines  71  of detector chip  55  in a spectrally split manner. A lens (not shown) can be arranged downstream of dispersive element  70 , which images the spatially split light in a suitable way onto the individual detector lines  71  of two-dimensional detector chip  55 . The exemplary embodiment shown here is an imaging spectrometer. 
         [0042]      FIG. 6   a  is a schematic representation of another embodiment of illumination device  65  in illumination beam path  20   1 . Illumination device  65  includes a digital modulator  66  (DMD) in illumination beam path  20   1  of light source  67 . Illumination device  65  is arranged in an illumination beam path  20   a . In the arrangement shown in  FIG. 9   a , illumination beam path  20   a  is inclined with respect to detection beam path  21   a , by an angle  41  or an angle  42 , respectively, with respect to normal  30  on surface  22  of wafer  23 . If angle  41  is equal to angle  42 , this is referred to as a bright-field arrangement. If angle  41  is not equal to angle  42 , this is referred to as a dark-field arrangement. The present embodiment has the particular advantage that the user can switch between the two arrangements according to the measuring problem. In one case, the bright-field arrangement may be better suited for solving a measuring problem than the dark-field arrangement, and vice versa. 
         [0043]      FIG. 6   b  is a schematic representation of a possible illumination pattern  85 , which can be created with the aid of DMD  66  on surface  22  of wafer  23 . In  FIG. 6   b  an illumination pattern  85  is shown which takes dies  64  arranged on surface  22  of wafer  23  into account. Illumination pattern  85  can also be configured in such a way, for example, that areas  86 , the so-called “streets” between dies  64 , are illuminated with a different intensity to the dies  64  themselves. It is also conceivable, that the areas of illumination pattern  85  may differ from each other with respect to their wavelengths and/or their intensities. 
         [0044]      FIG. 7  shows the spectral composition of the illumination light when illumination device  20  is configured as a spectral line light source. In  FIG. 5 , abscissa  82  is the wavelength λ, and ordinate  83  is the intensity I. It can be quite easily seen that the spectral line light source shows different peaks  80 , differing from each other in wavelength λ. It is obvious from the peaks formed with the spectral line light source that surface  22  of wafer  23  is spectrally illuminated. 
         [0045]    In  FIG. 8 , again, abscissa  9  is wavelength λ, and ordinate  91  is the intensity. The continuously adjustable light source shows an intensity characteristic  92 , essentially independent of wavelength λ. The continuously adjustable light source is controlled in such a way that a wavelength range or wavelength peak  93  selected by the user is emitted. Surface  22  of wafer  23  can then be illuminated with this wavelength peak  93  or this spectral interval. 
         [0046]      FIG. 9  shows the intensity of the illumination, when illumination device  20  is configured as an LED. Again, abscissa  100  is the wavelength % and ordinate  101  is the intensity. When only one type of LED is used an excellent peak  102  can be seen at wavelength λ. The surface of the wafer is then illuminated by this intensity peak. It goes without saying that LEDs may also be used which emit light at different wavelengths. It is obvious, that in the diagram of  FIG. 10  a plurality of intensity peaks would then be discernible at different wavelengths. 
         [0047]      FIG. 10  shows a broadband light source used with a filter, preferably a comb filter. First the broadband light source emits light which is essentially independent of wavelength λ. This is shown in  FIG. 11   a . In the figure, abscissa  110  is the wavelength λ, and ordinate  111  is the intensity I. The comb filter has the effect that light is transmitted only in a narrow wavelength range. As shown in  FIG. 11   b , in which, abscissa  110  is the wavelength λ, and ordinate  111  is the intensity I, the comb filter produces strong wavelength peaks at different wavelengths. The result of the broadband light source in combination with the comb filter is shown in  FIG. 11   c . Again, abscissa  110  is the wavelength λ, and ordinate  111  is the intensity I. When a three-band comb filter is used, the final result from the broadband light source, is a light characterized by three corresponding different wavelength peaks at different wavelengths. 
         [0048]    While the present invention was described with respect to a particular embodiment, it is obvious to the person skilled in the art that modifications and changes to the invention can be made without departing from the scope of the appended claims.