Abstract:
Examination devices and methods operating with incident light have hitherto been used for the examination of wafers. To allow these devices also to be used with the transmitted-light method, it is proposed to configure the substrate holder ( 16 ) so that an illumination device ( 38, 40, 42 ) is integrated into the substrate holder ( 16 ) in such a way that transmitted-light illumination of the wafer ( 18 ) is possible.

Description:
RELATED APPLICATIONS 
   This application claims priority of the German patent application 10 2004 015 326.4 which is incorporated by reference herein. 
   FIELD OF THE INVENTION 
   The invention concerns apparatuses for inspecting a semiconductor component, having a substrate holder on which the semiconductor component, which is a wafer or a microchip or a micromechanical component, is mounted for inspection. 
   The invention further concerns a method for inspecting a semiconductor component in which a substrate holder, on which the semiconductor component is mounted for inspection, is provided. The semiconductor component is observed with an observation device, in particular a microscope having at least one objective. 
   BACKGROUND OF THE INVENTION 
   Optical devices are particularly suitable for inspecting the surface of wafers. Examination of the surface can be accomplished, for example, as is known from EP 455 857, by evaluating rays that are reflected from the surface of the wafer. 
   Also known are optical apparatuses that, by image recognition, allow the detection of a great variety of features on the surface of a wafer or a semiconductor substrate. In this context the wafer is usually illuminated in bright-field fashion and scanned with a camera, for example a matrix camera or linear camera. 
   It is furthermore known from U.S. Pat. No. 6,587,193 to examine the surface of a wafer, an illumination being selected that scans the wafer in the form of a line. The illuminating line is guided over the surface of the wafer so that a two-dimensional image can be produced. 
   US 2003/0202178 A1 furthermore discloses a method and an apparatus for examining a wafer. Here an illumination is irradiated onto the wafer so that an edge of the wafer is struck. The edge of the wafer can thus be sensed and processed by an image processing unit. Defects of the wafer can be ascertained by a comparison of the ascertained edge image with a stored comparison image. 
   The known systems for inspecting a wafer are designed exclusively for incident-light inspection. The reason for this is principally that silicon wafers are opaque in the region of visible, ultraviolet, and deep ultraviolet light wavelengths. Silicon becomes transparent only at a wavelength above 1000 nm. In these wavelength regions the possibility then presents itself of being able to inspect features below the surface of the wafer, or to observe features on the front side of the wafer through the back side. 
   For the transmitted-light examination of wafers, however, the known illumination concepts of transmitted-light microscopy require a transmitted-light illuminating optical system below the microscope and a transmitted-light-capable microscope stage, which is not implemented in presently known examination systems. An expansion of the known examination systems to include transmitted-light inspection therefore requires a completely new design. In particular, such systems would need to be equipped with a wafer microscope stage suitable for transmitted light, which has, in contrast to the incident-light wafer microscope stages used hitherto, an unobstructed passthrough opening for the transmitted-light illumination over the entire wafer diameter. Considerable design effort for integrating a transmitted-light illumination system into the wafer inspection device is also necessary. 
   SUMMARY OF THE INVENTION 
   It is therefore the object of the present invention to develop the known wafer/semiconductor component inspection device so that it can be used for transmitted-light applications. 
   According to the present invention, this object is achieved by way of an apparatus for inspecting at least one semiconductor component comprising: a substrate holder that retains the semiconductor component for inspection and an illumination device for transilluminating the semiconductor component wherein the provided with the substrate holder. 
   It is a further object of the present invention to develop the known wafer/semiconductor component inspection method which can be used for transmitted-light applications. 
   The above object is accomplished by a method for inspecting a semiconductor component, comprising the steps of: 
   mounting the semiconductor component on a substrate holder for inspection, 
   observing the semiconductor component, with a microscope, having at least one objective for observing the semiconductor component, 
   illuminating the semiconductor component in a transilluminating fashion, wherein the substrate holder is equipped with an illumination device. 
   According to the present invention a special substrate holder is therefore provided, into which is integrated an illumination device for illuminating the wafer. The semiconductor component can encompass, for example, a wafer, a microchip, or a micromechanical component. It is self-evident that several microchips or micromechanical components are patterned onto one wafer. The term “wafer” is used for the sake of simplicity in the description that follows, but is not to be construed as a limitation. To allow the semiconductor component or wafer to be observed in transmitted light, the illumination device is embodied so that it emits light of a wavelength in the infrared wavelength region. The wafer is transparent to light in the infrared wavelength region. The substrate holder can be embodied as an attachment onto a wafer stage that is already present, if the geometrically required registrations are taken into account. The illumination device emits an illuminating light beam for illumination of the wafer. The wafer is thus illuminated from below, i.e. from the side facing away from the microscope&#39;s objective. This makes transmitted-light observation possible, while dispensing with any complex modification of the design of the overall equipment. In principle, with the apparatus and the method according to the present invention the possibility also exists of allowing observation, in transmitted light, of features in the deeper layers of the wafer and below the wafer surface. This is of great interest for quality control when packaging chips in the housing, since here the functional surface of the chip faces away from the housing surface. 
   In a preferred embodiment, a diffusion device is provided in order to achieve a high intensity and homogeneity in the illuminating radiation; for example, a diffusion panel; a diffusely scattering coating of, in particular, the side walls of the substrate holder; or a diffusely scattering collector optical system is used. The diffusion devices can be used singly or in combination with one another. 
   In an embodiment, the illumination device can encompass at least one light guide that is integrated into the substrate holder. Light of a suitable wavelength can then be guided through this light guide into the substrate holder. It is likewise possible to provide infrared light-emitting diodes, in particular in the form of a light-emitting diode matrix, in the substrate holder. The light-emitting diodes can be mounted directly on the inner side of the side wall of the substrate holder, or integrated into the latter. 
   For illumination of the wafer or semiconductor component, it is placed onto the substrate holder. An illuminating light beam emerges from the illumination device and then illuminates the wafer. Advantageously, the wafer is diffusely illuminated, i.e. before encountering the wafer the illuminating light beam is conveyed to a diffusion device, e.g. a glass carrier plate on which the wafer lies, a diffusion panel, a diffusely scattering coating, or a diffusely scattering collector optical system. 
   If the illumination device is appropriately selected, it can also be carried along in the interior of the substrate holder, so that a large-area configuration can be dispensed with. In particular, an incandescent lamp or a locally delimited light-emitting diode array, mounted on a positioning unit that is moved synchronously with the scanning stage, can be used here. 
   With the integrated illumination system, a wafer inspection device that permits transmitted-light illumination of the wafer is created. There is no need to redesign the scanning stage, the basic frame, or the microscope unit. On the contrary, units already on the market can in fact be retrofitted with the transmitted-light device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages and advantageous embodiments of the invention are the subject matter of the Figures below and their descriptions. 
     In the individual Figures: 
       FIG. 1  is a schematic overall view of a wafer inspection device; 
       FIG. 2  schematically shows a scanning stage with a wafer; 
       FIG. 3  schematically shows an embodiment of the substrate holder with light guides; 
       FIG. 4  schematically shows an embodiment of the substrate holder with light-emitting diodes; 
       FIG. 5  schematically shows an embodiment of the substrate holder with a movable, locally delimited illumination device; 
       FIG. 6  schematically shows an embodiment of the substrate holder with a locally delimited illumination device provided in stationary fashion. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically shows a characteristic configuration of a wafer inspection device  10  according to the present invention. A scanning stage  14 , constituting the microscope stage, is integrated on a basic frame  12 . Wafer  18  that is to be examined is placed onto or into scanning stage  14 , either directly or on a substrate holder  16  located on the scanning stage. An observation device, preferably a microscope  20 , is connected via a carrier unit  22  to basic frame  12  and allows magnified observation of wafer  18 . Microscope  20  encompasses at least one objective  24 , which represents an imaging optical system that make possible observation at different magnifications. The features observed in magnified fashion can be viewed directly via an eyepiece  26  or via a CCD camera  28  that is provided as applicable. The signals of camera  28  are transmitted for that purpose to a monitor  30 . Additionally provided is an electronics unit  32  with which system automation can be achieved. Electronics unit  32  serves in particular to control scanning stage  14  or to read out camera  28 . 
   Substrate holder  16  is usually configured so that it can receive the wafer or semiconductor component  18  under examination in such a way that is immobilized during the examination time period. According to the present invention, it comprises an illumination device that enables transmitted-light illumination of wafer  18 . 
   As shown in  FIG. 2 , scanning stage  14  comprises two axes  36  and  34  that are displaceable perpendicular to one another in the X and the Y direction. Every point  35  to be observed on wafer  18  can thus be brought beneath the optical axis of microscope objective  24  ( FIG. 1 ). Wafer  18  is immobilized on substrate holder  16 , and is illuminated by the illumination device integrated into substrate holder  16 . 
     FIG. 3  depicts substrate holder  16  in a first embodiment. Integrated into substrate holder  16  is an illumination device  38  that comprises at least one light guide  39 . Substrate holder  16  is closed at the bottom, i.e. on the side facing away from wafer  18 , and is open at the top, i.e. in the direction toward wafer  18 . Wafer  18  can be placed, for examination, on a glass plate  46 . Depending on requirements regarding the flatness of water  18  and the homogeneity of the illumination, however, the wafer can also be placed, without a glass plate, directly on substrate holder  16 . For this, the side edges of wafer  18  are placed into support edges  44  on both sides of substrate holder  16 . Small orifices through which a vacuum can be applied to wafer  18  can be provided in glass plate  46 , thus making possible immobilization of wafer  18 . 
   For illumination, light is guided through at least one light guide  39  into the interior of substrate holder  16 . The side walls along the periphery of substrate holder  16  are preferably selected as the entry points. Light guides  39  are oriented with an inclination from top to bottom but can also enter substrate holder  16  from bottom to top, or horizontally. An illuminating radiation  48  whose wavelength lies in the infrared emerges from light guide  39 . Illuminating radiation  48  is diffusely reflected at the inner walls of substrate holder  16  and thus travels from bottom to top, through glass plate  46  if applicable, through wafer  18 . To maximize the intensity and homogeneity, the inner walls of substrate holder  16  can be provided with a highly reflective diffusely reflecting layer, which then constitutes a diffusion device. At the exit surface of light guide  39 , a collector optical system  37  can be provided as a part of illumination device  38 . With that system, the emission characteristics can be optimally adapted to the geometric interior configuration of substrate holder  16 . In addition, collector optical system  37  itself can already have diffusely scattering properties that can be brought about, in particular, by way of a roughened surface. For better homogenization of illuminating radiation  48 , glass plate  46  can also have such diffusely scattering properties. 
   A further embodiment of the wafer stage is depicted schematically in  FIG. 4 . Light-emitting diodes  40  are provided here as the illumination device. The illuminating light is preferably produced entirely in the interior of substrate holder  16 , light-emitting diodes  40  arranged in planar fashion being provided on the floor of substrate holder  16 . An embodiment in which light-emitting diodes  40  are provided in the form of a planar light-emitting diode matrix is particularly suitable here. To improve illumination homogeneity in the plane of wafer  18 , a diffusion panel  50  can be arranged between light-emitting diodes  40  and wafer  18 . Alternatively or additionally, glass plate  46  can once again have diffusing properties. 
   Because undesirable heat occurs as a result of the operation of light-emitting diodes  40 , a further advantage can be achieved with the aid of a control device, for example electronics unit  32 . For this purpose, the control device controls light-emitting diodes  40  in such a way that only those particular diodes currently located beneath observation point  35  ( FIG. 2 ) emit light. The result is that heat evolution is greatly reduced even though illumination is adequate and homogeneous. Only a subset of the light-emitting diodes that are present is therefore used to illuminate wafer  18 . 
   The actions already cited for the homogenization of illuminating radiation  48  are to be regarded as examples. In general, all methods known for producing a homogeneous background illumination can be used, especially those that are applied in LCD flat-screen monitors. Glass plate  46  need not necessarily be made of glass. On the contrary, any material can be used that is transparent to the illuminating rays  48  utilized in each case. 
   A further embodiment of substrate holder  16  is depicted schematically in  FIG. 5 . The illumination device used in this embodiment is a locally delimited light source, for example a conventional incandescent lamp  42  or a locally delimited light-emitting diode array. Incandescent lamp  42  is positioned beneath the respective point  35  to be observed so that the latter is sufficiently illuminated. For that purpose, the incandescent lamp is brought to observation point  35 , preferably synchronously with the scanning stage, via an X-Y positioning unit  52  inside substrate holder  16 . In particularly preferred fashion, a unit that comprises the actual light source as well as a collector optical system having optionally diffusing properties in order to homogenize the illumination can be used as the illumination source. The illumination device can thus, concretely, comprise a locally delimited light-emitting diode array together with a collector optical system. 
   In a further preferred embodiment of substrate holder  16 , the locally delimited illumination source  42  can also be arranged in stationary fashion relative to microscope  20 . This is depicted in  FIG. 6 . Substrate holder  16  is embodied here not as a completely closed cylinder, but as a component that is U-shaped in cross section. As in all the embodiments hitherto described, substrate holder  16  can move together with scanning stage  14  ( FIG. 1 ) during positioning. Light source  42  is held on carrier arm  54  which is located between the limbs, i.e. the upper and the lower side, of the U-shaped substrate holder  16 . This ensures that carrier arm  54 , and therefore light source  42 , can be positioned as desired without resulting in collisions. An advantage of this embodiment is that an X-Y positioning unit can be eliminated, as can a large-area light-emitting diode array that generates a great deal of heat and entails high energy consumption. 
   Alternatively, illumination device  38  can be embodied as a light-guiding cable guided along carrier arm  54  and having a deflection and homogenization optical system mounted at the exit end, and an incoupling of light outside substrate holder  16  can be utilized.