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.
The present invention relates to an apparatus for wafer inspection. In particular, the present invention relates to an apparatus for the inspection of a wafer, including at least one illumination device for radiating an illumination light beam in an illumination beam path onto a surface of the wafer. Further, a detector is provided, which determines a detection beam path and has a predetermined spectral sensitivity. The detector records data of at least one illuminated area on the surface of the wafer. Herein the light coming from the surface of the wafer can have a plurality of different spectral ranges.
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.
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.
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.
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.
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.
An object of the present invention is to provide an apparatus, with which the detection speed and the detection sensitivity can be further improved.
The present invention provides an apparatus with at least one illumination device each arranged in an illumination beam path, wherein the at least one illumination device radiates an illumination spot onto a surface of the wafer and being a continuous light source. A detector is arranged in a detection beam path and has a predetermined spectral sensitivity. The detector records data from the at least one illumination spot from the surface of the wafer. An imager generates a relative movement between the surface of the wafer and the detector, whereby in a meandering movement the illumination spot is passed across the entire surface of the wafer in the scanning direction. The at least one illumination spot is detected in a plurality of different spectral ranges.
According to the present invention, an apparatus for inspecting the surface of a wafer is provided, the illumination device of which includes at least one continuous light source. In another embodiment, a polarizer is downstream of the illumination device in the illumination beam path.
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.
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.
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.
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.
In a further embodiment of the present invention, the illumination device and the detector are arranged such that the illumination beam path and the detection beam path are each inclined at an angle to the normal on the surface of the wafer. The inclined arrangement of the illumination device and the detector can be provided in a bright-field arrangement, which means that the angles at which the illumination beam path and the detection beam path are inclined to the normal on the surface of the wafer are equal. In the dark field arrangement, the angle at which the illumination beam path is inclined to the normal on the surface of the wafer differs from that at which the detection beam path is inclined.
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.
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.
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 >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.
a shows a detailed view of the arrangement, wherein the detector includes a trilinear detector;
b shows another embodiment of the detector, wherein the detector includes a plurality of detector chips;
c shows an embodiment of the detector, wherein the detector includes a two dimensional detector chip;
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;
b is a schematic representation of a possible illumination pattern created by means of the DMD on the surface of the wafer;
With reference to
a is a detail view of the arrangement, wherein the detector includes a trilinear detector. Detectors 211 or 212 includes three detector lines 501, 502 and 503, each of which is provided with a corresponding color filter 511, 512 and 513. Using the trilinear detector, it is therefore possible for each of the detector lines 501, 502 and 503 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 511, 512 and 513.
b shows another embodiment of detector 211 and/or 212, wherein the detector includes a plurality of detector chips 531, 532 and 533. Detector chips 531, 532 and 533 are arranged around a dispersive arrangement 54, for spectrally splitting the impinging light, so that the individual detector chips 531, 532 and 533 each receive different color information. In a particular embodiment, first detector chip 531 can detect red light, second detector chip 532 can detect green light and third detector chip 533 can detect blue light.
c shows an embodiment of detector 211 and/or 212, 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 21a1 or 21a2. Dispersive element 70 is for spatially separating the spectral portions of the detected light in detection beam path 21a1 or 21a2, 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.
a is a schematic representation of another embodiment of illumination device 65 in illumination beam path 201. Illumination device 65 includes a digital modulator 66 (DMD) in illumination beam path 201 of light source 67. Illumination device 65 is arranged in an illumination beam path 20a. In the arrangement shown in
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
In
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.
Number | Date | Country | Kind |
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102006059190.9-52 | Dec 2006 | DE | national |