Abstract:
A scanning probe microscopy device for mapping nanostructures on a sample surface of a sample is provided. The device may comprise a plurality probes for scanning the sample surface, and one or more motion actuators for enabling motion of the probes relative to the sample, wherein each of the plurality of probes comprises a probing tip mounted on a cantilever arranged for bringing the probing tip in contact with the sampling surface for enabling the scanning. The device may further comprise a plurality of Z-position detectors for determining a position of each probing tip along a Z-direction when the probing tip is in contact with the sample surface, wherein the Z-direction is a direction transverse to the sample surface, for enabling mapping of the nanostructures.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to an scanning probe microscopy device for mapping nanostructures on a sample surface of a sample, comprising a plurality probes for scanning the sample surface, and one or more motion actuators for enabling motion of the probes relative to the sample, wherein each of said plurality of probes comprises a probing tip mounted on a cantilever arranged for bringing the probing tip in contact with the sampling surface for enabling the scanning, the device further comprising a plurality of Z-position detectors for determining a position of each probing tip along a Z-direction when the probing tip is in contact with the sample surface, wherein the Z-direction is a direction transverse to the sample surface, for enabling mapping of the nanostructures. 
       BACKGROUND 
       [0002]    Scanning probe microscopy (SPM) devices, such as atomic force microscopy (AFM) devices as described above are for example applied in the semiconductor industry for scanning of semiconductor topologies on a surface. Other uses of this technology are found in biomedical industry, nanotechnology, and scientific applications. In particular, AFM may be used for critical defect metrology (CD-metrology), particle scanning, stress- and roughness measurements. AFM microscopy allows visualization of surfaces at very high accuracy, enabling visualization of surface elements at sub-nanometer resolution. 
         [0003]    The very high resolution and accuracy of this technology however comes at the cost of performance in terms of throughput. Atomic force microscopy is performed by tracing of a sample surface in a scanning motion using a probe tip touching or tapping (i.e. repeatedly touching) the surface, while accurately measuring disposition of the probe tip in a direction transverse to the sample surface (z-direction) using for example a high precision optical sensing system, e.g. using beam deflection or an interferometer. Scanning is performed by vibrating the tip in the z-direction, while performing the scanning motion across the surface to be mapped. To accurately map a given section of a sample surface, e.g. a structure on a wafer surface, the probe tip requires to be scanned such that every fraction of the section with sub-nanometer dimensions is touched or tapped by the probe tip at least once. As will be appreciated, this process may be rather slow. 
         [0004]    Further development of the SPM technology has provided AFM systems comprising a probe head upon which a plurality of probes are mounted side by side. Each probe comprises a cantilever and a probe tip, and each probe tips position in z-direction is measureable independently. This allows for scanning of a plurality of ‘scanning lanes’ at one pass of the scanning head, and as will be appreciated, the speed at which a single section may be scanned is multiplied by the number of probe tips present on the head. 
         [0005]    Even though the above has lead to an improvement in throughput, the scanning of multiple sites on a sample surface still takes a considerable amount of time. For this and other reasons, application of this technique in industrial environments, for example for the testing of wafers in semiconductor industry, is far from ideal. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present invention to alleviate the abovementioned problems of the prior art, and to provide a scanning probe microscopy device that allows for high speed high throughput scanning of multiple sites on a sampling surface. 
         [0007]    The above mentioned and other objects of the invention are achieved in that there is provided an scanning microscopy device for mapping nanostructures on a sample surface of a sample, comprising a plurality probes for scanning the sample surface, and one or more motion actuators for enabling motion of the probes relative to the sample, wherein each of said plurality of probes comprises a probing tip mounted on a cantilever arranged for bringing the probing tip in contact with the sampling surface for enabling the scanning, the device further comprising a plurality of Z-position detectors for determining a position of each probing tip along a Z-direction when the probing tip is in contact with the sample surface, wherein the Z-direction is a direction transverse to the sample surface, for enabling mapping of the nanostructures; wherein the plurality of probes are mounted on a plurality of heads, each head comprising one or more of said plurality of probes; wherein each of said heads is mounted on a support base associated with said head, each support base being arranged for individually moving its associated head relative to the sample; and wherein, for enabling said individual motion of the associated head, each support base comprises a plane actuator unit comprising at least one of said motion actuators for moving the head associated with the support base relative to the sample in at least one direction parallel to the sample surface, wherein the plane actuator unit is located at a first mounting position along said support base, said first mounting position being remote from a second mounting position, wherein the head associated with the support base is mounted on the second mounting position on the support base. 
         [0008]    The scanning probe microscopy device of the present invention may for example be an atomic force microscopy (AFM) device. Although in the present document reference will be made to particularly the embodiment of an atomic force microscopy device, the teachings of this document are not restricted to such an application, and may be applied to similar devices in the field of: BEEM, ballistic electron emission microscopy; CFM, chemical force microscopy; C-AFM, conductive atomic force microscopy; ECSTM electrochemical scanning tunneling microscope; EFM, electrostatic force microscopy; FluidFM, fluidic force microscope; FMM, force modulation microscopy; FOSPM, feature-oriented scanning probe microscopy; KPFM, kelvin probe force microscopy; MFM, magnetic force microscopy; MRFM, magnetic resonance force microscopy; NSOM, near-field scanning optical microscopy (or SNOM, scanning near-field optical microscopy); PFM, Piezoresponse Force Microscopy; PSTM, photon scanning tunneling microscopy; PTMS, photothermal microspectroscopy/microscopy; SCM, scanning capacitance microscopy; SECM, scanning electrochemical microscopy; SGM, scanning gate microscopy. 
         [0009]    In accordance with most embodiments, the support bases comprising the probe heads will be embodied as support arms. With respect to such embodiments, the term ‘support base’ used in this document is to be interpreted as ‘support arm’. As will be appreciated, the concept of the invention may be implemented using different type of support bases. 
         [0010]    A scanning probe microscopy device, such as an atomic force microscopy device, uses actuators for enabling motion of it&#39;s probing tips in three orthogonal directions relative the sampling surface. As already indicated, the tip must be movable in the z-direction which is usually implemented by applying a vibration to the probe tip in this direction. For scanning the surface, the probe tip is to be moved in two orthogonal directions parallel to the sampling surface. 
         [0011]    In accordance with the inventive principle, the actuators for moving a head comprising the at least one probe tip parallel to the sampling surface, are located remotely from the mounting position of the head on the support base or support arm. The plane actuator unit for moving the head in-plane with respect to the sampling surface is placed at a distance away from the head, where there is more room available for accommodating the actuators. This released constraints on the head, and enables to provide the head being much smaller. As a result, the inventive atomic force microscopy device can be equipped with multiple support bases or arms, each base carrying a head, and each head comprising one or more probes with probing tips. Each arm comprises its own plane actuator unit, allowing individual motion of each support base, independently from other bases. 
         [0012]    As a result, the atomic force microscopy device of the invention allows for the simultaneous scanning of multiple remote sites on a single sampling surface, where each site may be scanned at the typical scanning speeds of a conventional microscope. The throughput is therefore multiplied by the number of support bases or support arms applied, which reduces the processing time considerably. For example, suppose that a convention AFM method requires 40 seconds for scanning a single site of 10 μm*10 μm. A wafer comprising 50 sites to be tested will take more than half an hour when it is tested using the conventional AFM method. Suppose the inventive AFM method is applied in an AFM device with 50 individually movable and controllable support bases or arms, this wafer may be tested in only 40 seconds. As will be appreciated, the amount of support bases or arms provided is only limited by the design of the device, and is not restricted to the specific example of 50 bases or arms. A device with 30 bases or arms would require 80 seconds for scanning all sites: the first 30 sites in the first pass, and the remaining 20 sites in a second pass. 
         [0013]    In a specific embodiment, the first mounting position is located near a first end of the support arm, and wherein the second mounting position is located near a second end of the support arm. In this embodiment, the actuators may be placed aligned with the axial direction through the support arm, in the extended direction thereof. Most flexibility in the design is achieved in this manner, and it further allows more support arms to be placed adjacent each other (due to absence of actuators and control parts to the side of the support arms), thereby increasing throughput. 
         [0014]    Although in principle, any two orthogonal directions according to any coordinate system may be used, in accordance with an embodiment of the invention, for one or more of said support bases or arms, the plane actuator unit of each of said one or more support arms comprises at least one of an X-direction motion actuator and a Y-direction motion actuator. Here the X- and Y-direction may be perpendicular directions parallel to the sampling surface corresponding to a Cartesian coordinate system. 
         [0015]    In a particular embodiment, the X-direction actuator comprises a linear shift actuator for moving the second end along the X-direction. In another particular embodiment, the Y-direction actuator comprises a rotational actuator for pivoting the support base or arm such as to move the second end in the Y-direction. With respect to this latter embodiment, it is to be said that the pivoting action of the support bases or arms for providing the Y-directional motion avoids conflicts between support arms obstructing each other during scanning. 
         [0016]    According to a particular embodiment, the rotational actuator comprises a hinge element for rotating the support arm in a plane parallel to the sample surface in use, said hinge element cooperating with a further linear shift actuator for providing the rotating action of the support arm. This allows for a very precise positioning of the probe tip relative to the sampling surface in the Y-direction. Moreover, to even increase precision, in accordance with a further embodiment, the hinge element comprises at least one element of a group comprising a cross hinge, a Haberland hinge, or a hinge comprising one or more leaf springs. Furthermore, again for allowing high precision positioning of the probe tip, in some embodiments the further linear shift actuator cooperating with the hinge element is arranged for acting on said support arm in a direction parallel to an axial direction through the arm and in an off-axis position thereof such as to enable pivoting of the arm by means of the hinge element. 
         [0017]    In an atomic force microscopy device in accordance with embodiments of the invention, each support base or arm may further comprises a Z-direction actuator for moving the probing tip in the Z-direction. The Z-direction actuator may comprise a Z-positioning actuator for bringing the probing tip to and from the sample surface, and/or a Z-vibration actuator for vibrating the probing tip in the Z-direction adjacent the sampling surface for enabling said scanning of said sample surface. According to some embodiments, the Z-direction actuator is located at the second mounting position of the support base or arm, mounted on or near the head. Mounting the Z-direction actuator on the head allows for the very precise and accurate stroke required in this direction. 
         [0018]    Embodiments of the atomic force microscopy device in accordance with the invention may further comprise a motion control locator unit arranged for determining in use a current position of each of the heads relative to the sample surface in at least a direction parallel to the sample surface. As will be appreciated, the motion control locator allows for controlling motion of the support bases or arms by providing precise information on the location of each head and associated arm. This may be implemented in that the motion control locator unit comprises a grid formed by an arrangement of optical references, and wherein each head comprises an optical sensor for detecting the optical references, wherein said grid is arranged substantially parallel to the sample surface at an opposite position of the support bases or arms relative to the sample surface, such that the support bases or arms are in between the sensor grid and the sample surface in use. The references may comprise optically contrasting regions, e.g. reflective regions and absorptive regions. In conventional AFM methods, the location of the head (i.e. X-Y-position) is measured from the side of the sampling surface with optical sensors. In the present invention, an optical path from the side to some of the heads may become obstructed by other arms and heads. Therefore, a new type of locator unit has been developed for use in some embodiments of the invention where the above problem of obstructed view may play part. The location is measured using a grid at an opposite side of the arm and head with respect to the sampling surface in use. 
         [0019]    As will be appreciated, an atomic force microscopy device in accordance with the invention, may further comprise a sample carrier arranged for receiving said sample in use, such as a wafer. Moreover, in accordance with some particular embodiments, relative to a gravitational direction, the heads are located above the optical reference grid, and the sample carrier is located above the heads, wherein the sample carrier is arranged for exposing the sample surface at a side facing the heads. This is a very convenient arrangement of functional layers in the device, as having the sample carrier on top allows for easy access to the sample carrier such as to replace the sample efficiently. At the same time, having the optical reference grid directly underneath the arms, opposite to the sample surface allows for accurate determination of the location of the heads and the probe tips at close distance. As a further improvement, the support base associated with each head can be locked with high stiffness to the grid, thus providing a stable reference for the topography measurement. The term actuator used throughout this document may include any high precision actuator available and known to the skilled person, including piezo-electric actuators, stepper motors, and the like. 
         [0020]    According to a further embodiment, the plane actuation unit associated with each support base is mounted directly on the support base, providing actuation forces between the support base and a support structure below the support base. As will be appreciated, the above is a mechanical reversion of the earlier embodiments, falling within the scope of the claims. 
         [0021]    In accordance with another embodiment, the plurality of heads are mounted on a plurality of support bases, the support bases being arranged in a circular arrangement around a circumference of an area for receiving the sample for extending the support bases over or under the sample in use for enabling scanning of said surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention will further be elucidated by description of some specific embodiments thereof, making reference to the attached drawings. The detailed description provides examples of possible implementations of the invention, but is not to be regarded as describing the only embodiments falling under the scope. The scope of the invention is defined in the claims, and the description is to be regarded as illustrative without being restrictive on the invention. In the drawings: 
           [0023]      FIG. 1  schematically illustrates the working principle of a typical prior art atomic force microscope; 
           [0024]      FIG. 2  schematically illustrates the working principle of an atomic force microscope in accordance with the present invention; 
           [0025]      FIGS. 3A and 3B  schematically illustrate an atomic force microscopy device in accordance with the present invention; 
           [0026]      FIGS. 4A and 4B  schematically illustrate a support arm of an atomic force microscope in accordance with the invention; 
           [0027]      FIGS. 5A and 5B  schematically illustrate an enlarged view of a probe head in an atomic force microscope in accordance with the present invention; 
           [0028]      FIGS. 6A and 6B  schematically illustrate a further embodiment comprising a circular placement of arms in an atomic force microscopy device in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The scanning probe microscopy device of the present invention may for example be an atomic force microscopy (AFM) device. Although in the description below reference will be made to particularly the embodiment of an atomic force microscopy device, the teachings of this document are not restricted to such an application. As will be appreciated the teachings of the invention may be applied to any microscopy device that is based on the principles of scanning a surface region using a probe. Particular fields of applications have been mentioned earlier in this document. 
         [0030]      FIG. 1  schematically illustrates the working principle of a typical prior art atomic force microscope. In  FIG. 1 , a probe head  2  comprises piezo type drivers  3  for the X-, Y-, and Z-directional motion of a probe  8 . The probe  8  consists of a cantilever  9  having a probe tip  10  arranged for scanning a sample surface  5 . During scanning, a dither piezo (not shown) may drive the cantilever in vibrational mode, for example close to resonant frequency, to enable tapping of the probe tip on the surface. The manner of applying a vibrational motion to the probe tip is known to the skilled person. 
         [0031]    Scanning of the sample surface  5  is performed by moving the probe tip  10  in the X- and Y direction parallel to the sample surface  5  (or alternatively, by moving the substrate surface while maintaining the position of the probe tip fixed in the X- and Y-directions). The probe tip  10  is brought in close proximity to the surface  5  by means of a z-directional piezo driver. Once in the position, the probe tip  10  is vibrated in the z-direction such that it repeatedly touches the surface  5  during scanning thereof. At the same time, a laser  16  illuminates the probe tip with laser beam  15 . The precise position in the z-direction is determined using photo diodes  18  which receive the reflected laser beam  15 . 
         [0032]    The sample surface  5  is carried using a sample carrier  4 . Driving of the piezo drivers  3  located on the probe head  2  is performed using the detector and feedback electronics  20 . At the same time, the detector and feedback electronics  20  receive the detected z position as determined using photo diodes  18 . This principle allows for very precise mapping of surface elements, such as surface element  13  on the sample surface. As described herein above, since the mapping of the surface has to be performed with great precision, the speed at which the method is performed is rather slow. 
         [0033]      FIG. 2  schematically illustrates an atomic force microscope device according to the present invention.  FIG. 2  in particular illustrates the working principle of the AFM microscope of the present invention. In particular, AFM microscope of the present invention comprises a plurality of support arms  23 , each of the support arms  23  carrying a probe head  25 . The support arms  23  can be moved individually and independently from each other such that a plurality of sites  27  on the surface of the wafer  20  can be scanned by the plurality of arms  23  simultaneously. Although the AFM microscope illustrated in  FIG. 2  only comprises 10 arms, it may be appreciated that the number of arms is only limited by the design of the AFM microscope. The microscope may easily comprise 20, 30, 40, 50, 60, 70 or more arms dependent on the size of the apparatus and the specific implementation of the principles of the present invention in the AFM microscope according to the embodiments. 
         [0034]      FIG. 3   a  is a schematic illustration of an atomic force microscope device in cross section is provided according to an embodiment of the present invention. In  FIG. 3   a  only two of the fifty arms in this embodiment are illustrated. In  FIG. 3   a , a fixed frame  33  comprises a sample carrier  35  from which there is suspended a wafer  36  forming the sample surface to be scanned using the AFM microscope of the present invention. The elements  37  on either side of the sample carrier  35  provide for calibration of the arrangement, and for replacement of probe tips mounted on the respective probe heads  43  and  53  during the process. The AFM microscope  30  illustrated in  FIG. 3   a  comprises two support arms  41  and  51 . Each support arm ( 41 ,  51 ) is mounted on a linear shift actuator  39  and  50  respectively arranged for moving the arms  41  and  51  in the x-direction relative to the sampling surface on wafer  36 . The x direction is indicated by arrow  31 . The z direction is indicated by arrow  32  in  FIG. 3   a . Schematically illustrated in  FIG. 3   a  are the probes  45  and  55  comprising the probe tips for scanning the surface of the wafer  36 . Also schematically illustrated in  FIG. 3   a  is vision element  58  comprising an imaging unit  57  for visual inspection of the wafer  36  by an operator. 
         [0035]      FIG. 3   b  illustrates schematically a top view of the optical reference grid  48  including part of the support arms (e.g. arm  41 ). Visible in  FIG. 3   b  are the imaging unit  57  placed on the vision element  58 . As illustrated a linear shift actuator  59  allows for moving the imaging unit  57  around underneath the wafer  36 . 
         [0036]      FIG. 4   a  is s schematic illustration of a support arm  70  carrying a probe head  67  in an atomic force microscope device according to the present invention. The support arm  70  is moved in the x direction  74  by means of linear shift actuator  60 . The linear shift actuator  60  consists of two glider rails  63  and a moving element  64  that can be moved in the direction of the glider rails  63 . 
         [0037]    In addition thereto, the support arm  70  is further connected to a further linear shift actuator  65  which is moved back and forth by means of element  68 . The further linear shift actuator  65  cooperates with hinge element  66  such as to provide a rotational motion schematically indicated by arrows  67   a  and  67   b  in  FIG. 4   a . This enables to move probe head  69  of the support arm  70  in the y direction  73  such as to reach any site on the sample surface (not shown in  FIG. 4   a ). 
         [0038]    The hinge element  66  may be an elastic hinge, such as a cross hinge or a Haberland hinge. The specific position of the probe head  69  (in particular the probe tip (not shown)) can be monitored using the optical reference grid  72  underneath the probe head  69 . A side view of the schematic illustration of  FIG. 4   a  is provided in  FIG. 4   b . This illustrates the rails  63  upon which the linear shift actuator  64  moves the support arm  70  back and forth in the x-direction. On the head  69 , the z-direction actuator  78  is present. The z direction actuator  68  is operated for moving the probe tip  76  on the cantilever  75  of the probe upward and downward in the z direction such as to move it to and from the sample surface. The actuator  78  is further arranged for applying a vibration to the probe tip  76  in the z direction during scanning of the sample surface. This enables mapping of the sample surface in great detail. 
         [0039]      FIG. 5   a  illustrates schematically an enlarged view of the head  69  on the end of the support arms  70  in an atomic force microscope device according to the present invention. The head  69  comprises the z-direction actuator  78 . On the z-direction actuator  78 , a carrier construction  79  comprises a further piezo element  83  for vibrating the cantilever  75  and the probe tip  76 . Also illustrated is the laser  15  used for accurately monitoring the z-position of the probe tip  76  upon touching the surface of the sample. 
         [0040]    Underneath the head  69  two encoder heads  80  and  81  cooperate with the optical reference grid  72  for accurately determining the position of the probe head  69 . The probe head  69  rests on the optical reference grid plane  72  by means of an air bearing, i.e. by blowing air through small pinholes in the surface  72 .  FIG. 5   b  illustrates the foot print of probe head  69  on the surface  72 . In  FIG. 5   b , encoder heads  80  and  81  and the z-direction actuator can be seen. In the invention, the support bases and other components are located in a general fixed frame with sufficient mechanical and thermal stiffness. 
         [0041]      FIGS. 6A and 6B  schematically illustrate a further embodiment comprising a circular placement of arms in an atomic force microscopy device in accordance with the present invention. In  FIG. 6A , a wafer  20 ′ is being examined using an atomic force microscope (AFM) in accordance with an embodiment of the invention. The AFM device comprises a plurality of arms  23 ′ that are placed in a circular arrangement around the circumference of the wafer  20 ′. Although schematically,  FIG. 6A  only depicts a total six arms  23 ′ part of the arms are omitted in the drawing in order not to obscure the comprehensibility of  FIG. 6A . In practice, any number of arms  23 ′ may be placed around the wafer  20 ′, not only in a part of the circumference but across its full circumference. 
         [0042]    The radial arrangement of the arms  23 ′ and the heads  25 ′ attached thereto, allows for a large number of arms to be placed around the wafer (more than 50 heads if desired). Since the throughput of the AFM microscope multiplies with the number of heads (scanning with two heads is twice as fast as compared to scanning with one head), the system in accordance with this embodiment has a very large throughput for scanning wafers. Such a system may therefore be advantageously applied in an industrial environment (although it is not limited thereto). Moreover, the circular arrangement automatically provides sufficient space at the back end of the arm (outside the scanning area) where the actuator are placed. 
         [0043]      FIG. 6B  schematically illustrates how the arms are operated for enabling most efficient scanning of the whole surface without clashing of the arms in the second embodiment. The arrow  90  points from the edge of the wafer towards the center. In this direction the radius decreases, and therefore the chance of clashing usually increases. At the same time however, surface area to be scanned decreases and therewith the number of areas to be scanned also decrease. The arms are extended in a staggered manner. Arms  23 ′- 2  and  23 ′- 4  have their heads  25 ′- 2  and  25 ′- 4  scanning in the peripheral area of the wafer. In an area more closer to the center, arms  23 ′- 1  and  23 ′- 5  with respective heads  25 ′- 1  and  25 ′- 5  are actively scanning the surface. In the area most close to the center and in the center itself, head  25 ′- 3  of arm  23 ′- 3  is active. 
         [0044]    The present invention has been described in terms of some specific embodiments thereof. It will be appreciated that the embodiments shown in the drawings and described here and above are intended for illustrative purposes only, and are not by any manner or means intended to be restrictive on the invention. The context of the invention discussed here is merely restricted by the scope of the appended claims.