Abstract:
An easy to use scanning probe instrument such as a microscope or memory device is provided with a probe which does not require optical alignment. The scanning probe is a cantilever probe adapted to undergo relative movement with respect to an object such as a sample or a recording media. Optical interference and/or displacement of the cantilever probe caused by interaction with the object while the probe is being scanned across the object is measured to determine characteristics of the object. The cantilever probe has a base member, a cantilever formed in the base member, at least a portion of the cantilever being elastically deflectable to enable the cantilever to be displaced in a given direction. A waveguide extends through the base member and has one end surface disposed proximate the cantilever, the one end surface being positioned perpendicularly with respect to the given direction of displacement of the cantilever and being spaced from the cantilever by a distance sufficient to allow displacement of the cantilever by a desired amount in the given direction.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a scanning atomic force microscope and scanning proximity field optical microscope for observing microscopic surface geometry or physical information, and to a memory device used to perform data recording and reading out. 
     Conventionally, in the probe microscope the detection of displacement using the action of a force between a probe and a sample has been an important technology in conducting distance control between the probe and the sample. Among the conventional distance control means are an optical lever method or an optical interference method using light, and further a self-detection type probe using a piezoelectric element is known, and so on. 
     The conventional optical lever method or optical interference method required a positioning mechanism to align an optical axis with the probe, together with difficultly in optical axis adjustment operation. There has been a problem in that the self-detection type probe using a piezoelectric element was complicated in the probe manufacture process. Furthermore, there has been a demand for a probe having a higher resonant frequency in order to carry out scanning at high speed. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a scanning probe which does not require optical axis alignment but is easy to use and high in resonant frequency, an atomic force microscope and scanning proximity field optical microscope which is easy to use and capable of high speed scanning, and a memory device which is easy to adjust and capable of high speed reading in. 
     As a scanning probe easy to use and high in scanning speed, a scanning probe was devised comprising: a cantilever probe; and a waveguide provided in proximity thereto; wherein a base portion of a cantilever or the cantilever itself is elastically deflectable to enable the cantilever to dynamically displace; the waveguide having an end surface positioned perpendicularly to a direction of displacement of the cantilever probe and at a distance not to prevent the displacement of the cantilever; and the cantilever probe and the optical waveguide being integrally formed on a common base member. 
     Furthermore, a scanning probe microscope was devised which is structured by at least this probe, an optical interference detecting means, a relative moving means between the probe and the sample, and a control and data processing means. 
     Also, a memory device was devised which is structured by at least this probe, a recording media, an optical interference detecting means, a relative moving means between the probe and the recording media, and a control and data processing means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is view showing a structure of a probe of the present invention; 
     FIG. 2 is a view showing a structure of a probe of the present invention; 
     FIG. 3 is a view showing a structure of a probe of the present invention; 
     FIG. 4 is a view showing a structure of a probe of the present invention; 
     FIG. 5 is a view showing a structure of a probe of the present invention; 
     FIG. 6 is a view showing a structure of a probe of the present invention; 
     FIG. 7 is a view showing a structure of a scanning probe microscope of the present invention; 
     FIGS. 8A and 8B are views showing a structure of an optical interference detecting means used in the scanning probe microscope of the present invention; 
     FIG. 9 is a view showing a structure of a scanning proximity field optical microscope of the present invention; 
     FIG. 10 is a view showing a structure of a scanning proximity field optical microscope of the present invention; 
     FIG. 11 is a view showing a structure of a memory device of the present invention; 
     FIG. 12 is a view showing a structure of a memory device of the present invention; and 
     FIG. 13 is a view showing a structure of a probe of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now embodiments of the present invention will be described with reference to the drawings. 
     FIG. 1 shows one example of a scanning probe according to the present invention. In FIG. 1, a probe of the invention has a cantilever probe  1  possessing a spring characteristic and mechanically displaceable, and being an optical waveguide formed by a core  2  and a clad  3 . The wave guide has its end face  4  positioned perpendicular with respect to a displacement direction of this cantilever probe  1 . Due to this, when light is emitted from the waveguide end face, it is reflected on the cantilever probe  1  and returns again to the waveguide end face  4 . Because interference occurs between the return light reflected on the cantilever probe and the return wave reflected on the waveguide end face, it is possible to detect deflection in the cantilever  1  from a change in a return wave signal intensity. Here, where the reflected return wave from the waveguide end face is weak, a reflection function can be separately provided together with an external signal source. Here, where utilizing wave interference using return waves from the waveguide end face, the sensitivity of interference varies at a period of an integral number of times a wavelength for a distance between the waveguide end face and the lever. Accordingly, it is possible to determine a gap distance by previously considering the above or finely adjust the interval by a thermal method. 
     The gap between this waveguide end face  4  and the cantilever probe  1  is preferably as small as possible. It is however required to be arranged in a positional relationship so as not to obstruct cantilever probe displacement. An important point of the invention lies in the fact that the cantilever probe  1  and the waveguide are integrally formed on a common base member  5 . This makes it possible to omit positional adjustment of the waveguide for the cantilever probe in every measurement. 
     As shown in FIG. 1, the cantilever probe  1  is formed with a sharp tip  6 . This tip is placed opposite to a position of the waveguide end face with respect to a direction of cantilever displacement. Thus the tip can function as an atomic force microscopic probe to detect a sample-to-probe acting force as a displacement in a distance direction. 
     The above scanning probe can be manufactured through a conventional semiconductor lithographic process or thin film forming process. 
     On the other hand, it is possible to structure the probe such that a sharp tip  7  is positioned coincident with a lever axis direction as shown in FIG.  2 . In this case, it is possible to utilize as a shear-mode probe for the scanning probe microscope. 
     In the embodiment shown in FIG. 3, a cantilever probe  8  has therein a waveguide  10  formed to have a wave traveling axis coincident with that of the waveguide  9 , whereby the optical waveguide has an end constituting a probe tip  11 . 
     In the above examples, an optical waveguide can generally be used as a waveguide. In such a case, most of the light traveling through the waveguide  9  propagates into the waveguide  10  and exits through the tip  11 . Accordingly, this scanning probe can be utilized as a proximity field optical microscopic probe to radiate light through the probe tip onto a sample. 
     An optical fiber can be used as an optical waveguide. FIG. 4 shows an embodiment using an optical fiber as a base material for a scanning probe. In this case, an optical waveguide provided is an optical fiber itself which is formed by a clad  12  and a core  13 . In order to form a cantilever probe  14 , the optical fiber is partly removed of an intermediate portion slightly distant from its end in an area at least about two-thirds of the diameter. The removal of the optical fiber intermediate portion can be realized by using techniques of a dicing saw, excimer laser, focused ion beam, etc. 
     In the embodiment of FIG. 4, a core-tipped sharp shape  15  is formed in the cantilever probe portion  14  of the optical fiber, for utilization as a probe for a proximity field optical microscope. This sharp shape can be formed by heating with a heater, burner or carbonic acid gas laser while applying tension at respective ends, or etching using hydrogen fluoride. 
     The probe for a proximity field optical microscope thus constructed has its lever portion made smaller as compared to the conventional optical-fiber probe utilizing elastic deflection in the fiber axial direction. Accordingly, the resonant frequency can be raised. Due to this, it can cope with a higher scanning rate. 
     In this proximity field optical microscope, the taper portion except for the sharp formed tip  16  is coated with a light shield material  17  as shown in FIG. 5 in order to narrow an area through which light is to be emitted. Specifically, the coating material can be a metal such as aluminum, chromium or gold. Further, a scanning sensor probe can be structured by fixing a sensor device  18  to detect temperature, magnetism, potential, light or the like as shown in FIG. 6 without sharpening the cantilever probe portion of the optical fiber. Here, the signal of the sensor device  18  may be extracted through a lead wire  19  or a patterned wire may be formed on the surface of the probe base member  5 . 
     Now a description is made of a scanning probe microscope using a scanning probe according to the present invention. 
     FIG. 7 illustrates a structural example of a scanning probe microscope in accordance with the present invention. In FIG. 7, a scanning probe microscope is structured by a scanning probe  50  as shown in FIG. 1, an optical interference detecting means  52 , a probe-sample relative movement means  53  and a control and data processing means  54 . The scanning probe  50  has an optical waveguide to which light is introduced from the optical interference detecting means  52 . The optical interference detecting means  52  also receives light returning from the same optical waveguide so that it can detect a displacement of the probe depending on the variation of optical intensity in interference. The signal detected therein is sent to the control and data processing means  54 . The scanning probe  50  has its sharp probe tip positioned in proximity to a sample  55  so that distance control between the probe and the sample as well as two dimensional scanning can be performed by the probe-sample relative movement means  53 . This relative movement means  53  is controlled by the control and data processing means  54 . The control and data processing means  54  converts a surface geometric signal into image information. Incidentally, where the scanning probe  50  is used with vibration, such probe vibration can be given by a piezoelectric vibrating means  49 . 
     FIGS. 8A and 8B illustrate a structural example of the optical interference detecting means  52 . In FIG. 8A, the light emitted from the light source  61  transmits through a beam splitter  62  and goes via a lens  63  into a waveguide of a scanning probe  64 . The light on the other hand is perpendicularly changed in direction by the beam splitter  62  to emit onto the mirror  65 . The light returning from the scanning probe  64  is perpendicularly changed in direction by the beam splitter  62 , reaching a light detector  66 , while the light reflected on the mirror  65  transmits through the beam splitter  62  to the light detector  66 . There is interference between the light portions reaching the light detector  66 . However, the return light from the probe is varied in phase by a displacement of the cantilever probe whereby its optical intensity is varied depending upon a displacement of the cantilever probe. 
     In FIG. 8B, the light from a light source  67  is introduced through a lens  68  into an optical fiber  69  connected to a 2-to-2 coupler  70 . The introduced light travels through the coupler  70  to the scanning probe  71 , part of which is branched into another optical fiber having a reflection end  72 . The return light from the probe is introduced through the coupler  70  to the light detector  73  while the light reflected on the reflection end  72  also introduced to the light detector  73 . Thus interference occurs between these light portions. Also in this case, the return light from the probe is varied in phase by a displacement of the cantilever probe. Accordingly, the optical intensity is varied depending upon a displacement of the cantilever probe. 
     The sensitivity of detection can be raised by modulating the light from the light source  61  or  67  and performing lock-in detection on the output of the light detector. 
     FIG. 9 shows an overall structural view of a scanning proximity field optical microscope using a proximity field optical microscope scanning probe  46  as shown in FIG. 3 or FIG.  4 . In FIG. 9, a focusing optical system  74  or  75  and a light detector  76  or  77  are added in addition to the FIGS. 8A and 8B structure. Light is emitted from a probe tip onto a sample  55  where part of the light transmits to be focused by an optical system  74 , being detected by a light detector  76 . On the other hand, the light reflected on the sample surface is focused by an optical system  75  and detected by a light detector  77 . In this case, a light for optical interference can be used as the detection light. However, physical property measurement on the sample can be implemented by preparing different-wavelength light sources for physical property measurement and arranging a filter  47  or  48  in front of the detector. 
     FIG. 10 shows an example of the structure of a so-called illumination collection mode as an application of a scanning proximity field optical microscope. In FIG. 10, added to the structure of FIG. 8A are a dichroic mirror  79  that reflects a light with a wavelength from the light source  61  for probe displacement detection but transmits a light with a wavelength from the light source  78  for sample physical property measurement, a dichroic mirror  80  that reflects the wavelength light from the probe displacement detecting light source  61  but transmits the wavelength light from the sample physical property measuring light source  78 , a filter or spectroscope  81  that selects an arbitrary wavelength for physical property measurement, and a photo detector  82 . The light path for probe displacement detection is similar to that of the FIG. 8B structure except for passing through the dichroic mirror on the course. The light for probe displacement measurement is emitted from the probe tip  51  onto a surface of a sample  55 . The light is converted into fluorescent or Ramman scatter light on a surface of a sample, part of which again returns through the probe tip  51  to the optical waveguide and then passes via the beam splitter  62  and the dichroic mirror  80  to the filter or spectrometer  81  for selecting an arbitrary wavelength for physical measurement, being detected by the light detector  82 . 
     Now an example is shown of the structure of a memory device using a scanning probe as shown in FIG.  1 . In FIG. 11, a memory device is structured by a scanning probe  91 , an optical interference detecting means  92 , a probe-recording media relative movement means  93 , a recording media  94 , a rotation means  95  and a control and data processing means  96 . This scanning probe  91  can read out information recorded in a surface form on the recording media  94 . 
     FIG. 12 is a structural example of a optical memory device using a proximity field optical microscope scanning probe as shown in FIG. 3 or FIG.  4 . In FIG. 12 there is provided, in place of the optical interference detecting means  92  in FIG. 11, an optical interference detecting means, a polarizing filter  97  for polarization change component detection and a light detector  98  for detecting intensity of the same light, in order to detect a change in polarization characteristic in the media. 
     The probe used for this memory can be structured by integrating a plurality of scanning probes. FIG. 13 shows a structural example of such a probe section. By incorporating this probe-integrated structure in a memory device, high speed processing is made possible. 
     According to the present invention, it became possible to provide a scanning probe which does not require optical axis alignment but is easy to use. This makes it possible to provide an atomic force microscope and scanning proximity field optical microscope that are easy to use. Because the probe of the invention is higher in resonant frequency than the conventional probe, a sample surface can be observed through scanning at a higher speed. Moreover, a memory device easy to adjust and able to scan at high speed can be obtained.