Abstract:
A multiprobe device is provided for a scanning probe instrument and has a plurality of individually-selectable probe members for conducting scanning probe operations. The multiprobe has a plurality of cantilever probes supported by a support member. Each of the cantilevers is individually-selectable for use in conducting scanning probe operations, and each has a different resonance frequency from the others. In a preferred embodiment, portions of the respective cantilevers that are brought into contact with a sample to conduct scanning probe operations are arranged in a substantially linear configuration. A given one of the cantilevers is selected by vibrating the multiprobe at the resonance frequency of the given cantilever.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multiprobe formed by providing a plurality of cantilevers on the same body in such a manner to allow selective use of each cantilever and to a scanning probe microscope utilizing the same. 
     2. Description of the Related Art 
     In scanning probe microscopes that are conventionally used for finding changes in a surface configuration, a physical quantity and the like of a microscopic region on the order of atoms, a probe which has a scanning needle on an end thereof or which has no such needle has been used as a scanning probe. In general, a probe of this type is fabricated in a cantilevered configuration to measure a configuration or the like of a surface of a sample by detecting the deflection of a cantilever due to an attraction force or repulsion force originating from an interatomic force generated between the surface of the sample and the scanning needle while when the cantilever is scanned across the sample surface. 
     A cantilever as described above must be replaced with a new one appropriately depending on the period of use because it is a wearable component, and it may be required to modify the cantilever depending on the purpose of measurement. There has been a problem in that the replacement of a probe is difficult and troublesome because it is a very small component. In order to solve this problem, multiprobes have been used which are formed by providing a plurality of cantilevers on the same body. 
     Known configurations of conventional multiprobes used for such a purpose include a configuration wherein a piezoelectric element for switching is provided for each of a plurality of cantilevers provided on the same body and those piezoelectric elements are selectively driven to allow only a desired cantilever to scan a surface of a sample and a configuration wherein a plurality of cantilevers are provided with different lengths and are sequentially used in the order of their decreasing lengths with cantilevers once used being broken and removed (or wherein long cantilevers are broken to prevent them from hindering the use of a desired cantilever). 
     However, the above-described known configurations have a problem in that the cost of a probe is increased by a complicated structure and operation attributable to the need for a switching mechanism utilizing a piezoelectric material such as ZnO and PZT and in that a need for a control system for selecting cantilevers leads to an increase in cost. 
     The latter configuration also has a problem in that the need for breaking unnecessary cantilevers reduces ease of operation and in that cantilevers can be broken by mistake when unnecessary cantilevers are broken because the component is very small and this makes it difficult to treat the component. 
     It is an object of the invention to provide a multiprobe in which the above-described problems with the prior art can be solved and a scanning probe microscope utilizing the same. 
     SUMMARY OF THE INVENTION 
     In order to solve the above-described problems, according to the invention, there is provided a multiprobe used as a scanning probe of a scanning probe microscope formed by providing a plurality of cantilevers on the same body, characterized in that the plurality of cantilevers have resonance frequencies different from each other and in that portions of the plurality of cantilevers to contact with a sample are arranged in a substantially liner configuration. 
     Since the plurality of cantilevers provided on the same body have resonance frequencies different from each other, when the multiprobe is operated in a DFM mode, it is possible to put only a required cantilever close to a surface of a sample to involve it in measurement by applying vibrations having the resonance frequency of the cantilever required for the measurement to the multiprobe thereby causing only the required cantilever to vibrate with an amplitude greater than those of the rest of the cantilevers as a result of resonance. That is, the multiprobe is operated in a DFM mode; the plurality of cantilevers are provided with peaks of resonance which are different from each other to such a degree that an operating point can be fixed; and the frequency of vibrations for external excitation is made substantially equal to the resonance frequency of a cantilever to be selected to involve only the cantilever in measurement as a result of an increased vibration amplitude. This makes it very easy to operate the plurality of cantilevers selectively. 
     While it is not required to provide each of the cantilevers with a scanning needle, since portions of the cantilevers to contact with a surface of a sample are arranged in a substantially linear configuration, the contact portions of those cantilevers are at similar distances to the sample during approach. 
     A self-detection type probe may be provided having a configuration as described above in which each of the plurality of cantilevers incorporates a distortion sensor for detecting deflection of the cantilever. In this case, the distortion sensors are set at the same characteristics. 
     The present invention proposes a method of measurement in which the distortion sensor of at least one cantilever uninvolved in measurement is used as a reference distortion sensor for measuring the output of the distortion sensors of the cantilevers involved in the measurement to improve the signal-to-noise ratio of the measurement. 
     An alternative configuration is possible in which a reference cantilever is separately provided and in which the reference cantilever is equipped with a distortion sensor similar to those of cantilevers for measurement as a reference distortion sensor. 
     The present invention proposes a scanning probe microscope which utilizes a multiprobe as described above and in which cantilevers can be selected and switched by substantially matching the frequency of vibration applied to the multiprobe with resonance frequency of a desired cantilever of the multiprobe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged plan view of a major part of an embodiment of a multiprobe according to the invention. 
     FIG. 2 is a characteristics diagram showing resonance frequency characteristics of the multiprobe shown in FIG.  1 . 
     FIG. 3 is an enlarged plan view of a major part of another embodiment of a multiprobe according to the invention. 
     FIG. 4 is a characteristics diagram showing resonance frequency characteristics of the multiprobe shown in FIG.  3 . 
     FIG. 5 is an enlarged plan view of a major part of still another embodiment of a multiprobe according to the invention. 
     FIG. 6 is an enlarged plan view of a major part of the multiprobe in FIG. 1 showing a more specific configuration of the same. 
     FIG. 7 is a circuit diagram of an example of a circuit configuration for measuring a sample utilizing the multiprobe shown in FIG.  6 . 
     FIG. 8 is an enlarged plan view of a major part of the multiprobe shown in FIG. 7 showing a more specific configuration of the same. 
     FIG. 9 is a block diagram of an example of a configuration of a scanning probe microscope utilizing the multiprobe shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An embodiment of the present invention will now be described in detail with reference to the drawings. 
     FIG. 1 is an enlarged view of a major part of an embodiment of a multiprobe according to the present invention. A multiprobe  1  is used as a scanning probe of a scanning probe microscope used for finding changes in a surface configuration, a physical quantity and the like of a microscopic region on the order of atoms and has three cantilevers  3 ,  4  and  5  provide on a body  2 . 
     The cantilever  3  is provided on the body  2  such that it extends from the body  2  with a width W 1  and a length t 1 . The cantilever  4  has the width W 1  at the end thereof and has a width W 2  greater than the width W 1  at the base thereof, and the region with the width W 1  has a length t 2  (&lt;t 1 ). The cantilever  5  has the width W 1  at the end thereof and has a width W 3  greater than the width W 1  at the base thereof, and the region with the width W 1  has a length t 3  (t 1 &gt;t 3 &gt;t 2 ). W 2  is equal to W 3  in the present embodiment. 
     Since the cantilevers  3 ,  4  and  5  have the above-described configurations, respective resonance frequencies f 3 , f 4  and f 5  substantially depend on the lengths of the regions having the width W 1  and satisfy the following relationship. 
     
       
         f 3 &lt;f 5 &lt;f 4   
       
     
     Spring constants k 3 , k 4  and k 5  of the cantilevers  3 ,  4  and  5  also depend on the lengths of the respective regions having the width W 1  and satisfy the following relationship in terms of the magnitudes thereof. 
     
       
         k 3 &lt;k 5 &lt;k 4   
       
     
     Reference symbols D 3 , D 4  and D 5  respectively represent scanning needles of the cantilevers  3 ,  4  and  5  which are portions of the cantilevers  3 ,  4  and  5  to contact with a sample. The scanning needles D 3 , D 4  and D 5  are all located at a distance from a reference surface  2 A of the body  2 . As a result, the scanning needles D 3 , D 4  and D 5  are arranged on a straight line L to provide a linear configuration. Obviously, cantilevers without scanning needles may be used which have no scanning needle and contact with a sample in a part of the ends thereof. In this case, the portions of the cantilevers to contact a sample may be arranged in a linear configuration. 
     FIG. 2 is a diagram showing resonance frequency characteristics of the multiprobe  1 . As shown in FIG. 2, there are peaks of resonance at the resonance frequencies f 3 , f 4  and f 5  of the respective cantilevers  3 ,  4  and  5 . Therefore, the cantilevers  3 ,  4  and  5  can be selectively used by setting operating points P 3 , P 4  and P 5  in the vicinity of the respective peaks of resonance. 
     Since the multiprobe  1  has the three cantilevers  3 ,  4  and  5  having resonance frequencies and spring constants different from each other as described above, when external vibrations are applied to the multiprobe  1  to cause the multiprobe  1  to operate in a DFM mode, only a desired cantilever can be used for measurement of a sample (not shown) by substantially matching the frequency of the vibrations with the resonance frequency of the desired cantilever to be used for the measurement to cause the desired cantilever to vibrate with an amplitude sufficiently greater than those of the other cantilevers. 
     It is therefore possible to select a cantilever having a desired spring constant for measurement by simply changing the frequency of vibrations applied to the multiprobe  1  without a need for a complicated switching mechanism utilizing a piezoelectric element. This eliminates a need for troublesome operations for replacing cantilevers as in the prior art and allows continuous measurement using three kinds of cantilevers having different spring constants by simply changing the frequency of vibrations for excitation. 
     Since the scanning needles D 3 , D 4  and D 5  of the cantilevers  3 ,  4  and  5  are in a linear configuration in which they are arranged on a straight line L, the scanning needles D 3 , D 4  and D 5  can be located at similar distances from a sample during an approaching operation in which the multiprobe  1  is caused to approach the sample. As a result, the approaching operation can be similarly performed regardless of which of the cantilevers  3 ,  4  and  5  is selected and used. 
     Since the multiprobe  1  has characteristics as described above, a cantilever having an optimum spring constant can be easily selected in accordance with the hardness and quality of the sample. With an appropriate number of cantilevers having different spring constants prepared on the same body, it is possible to perform optimum measurement for a sample by simply changing the frequency of vibrations for excitation. 
     FIG. 3 shows another embodiment of a multiprobe according to the present invention. A multiprobe  11  shown in FIG. 3 is also formed by providing three cantilevers  13 ,  14  and  15  on a body  12 . However, the lengths t 13 , t 14  and t 15  of regions having a width W 1  of the cantilevers  13 ,  14  and  15  are not significantly different from each other, and they have substantially equal spring constants. They are characterized in that their resonance frequencies are similar but are different from each other to a degree at which their respective peaks of resonance can be discriminated from each other. 
     FIG. 4 shows resonance frequency characteristics of the multiprobe  11 . While resonance frequencies f 13 , f 14  and f 15  of the respective cantilevers  13 ,  14  and  15  are rather close to each other compared to those in FIG. 1, respective operating points P 13 , P 14  and P 15  can be discriminated from each other, and spring constants k 13 , k 14  and k 15  of the respective cantilevers  13 ,  14  and  15  are substantially equal to each other. 
     Thus, in the multiprobe  11  shown in FIG. 3, the differences between the lengths t 13 , t 14  and t 15  of the regions having the width W 1  of the cantilevers  13 ,  14  and  15  are smaller than those in the embodiment shown in FIG.  1 . As a result, the resonance frequencies f 13 , f 14  and f 15  are closer to each other, and the spring constants k 13 , k 14  and k 15  are substantially equal to each other. Scanning needles D 13 , D 14  and D 15  of the respective cantilevers  13 ,  14  and  15  are also arranged in a linear configuration. 
     Since the multiprobe  11  has the above-described configuration, the cantilevers  13 ,  14  and  15  can be sequentially and selectively used for measurement by changing the frequency of vibrations applied to the multiprobe  11  slightly step-by-step to f 13 , f 14  and f 15 . It is therefore possible to sequentially and selectively use the cantilevers having substantially equal spring constants for measurement to measure a sample continuously by performing the measurement with the frequency changed slightly step-by-step. 
     As apparent from the above description, the multiprobe  1  is suitable for measurement using a cantilever selected for an optimum spring constant, and the multiprobe  11  is suitable for performing measurement continuously for a long period of time under constant conditions with cantilevers switched. 
     Both of the multiprobes  1  and  11  are advantageous in that an approaching operation is simplified because of the linear configuration of the scanning needles which allows any of the scanning needles to be kept at the same distance from a sample during the approaching operation to put the cantilevers in the first contact with the sample. 
     FIG. 5 shows still another embodiment of a multiprobe according to the present invention. A multiprobe  21  has cantilevers  23 ,  24  and  25  having the same width W 1  and different lengths provided on a body  22 . The cantilevers  23 ,  24  and  25  have lengths t 23 , t 24  and t 25  respectively (t 23 &lt;t 24 &lt;t 25 ), and scanning needles D 23 , D 24  and D 25  are arranged on a straight line M at the respective ends to provide a linear configuration. 
     In the multiprobe  21 , since the bases of the cantilevers  23 ,  24  and  25  are aligned with the level of a lateral surface  22 A of the body  22 , the intervals between the cantilevers  23 ,  24  and  25  can be smaller than those in the configurations of the embodiments shown in FIGS. 1 and 3 in which wider regions are provided at the bases to prevent the occurrence of crosstalk, which is advantageous in achieving compactness. The multiprobe  21  can be used similarly to the multiprobe  1  or  11  by setting the lengths of the cantilevers  23 ,  24  and  25  appropriately. 
     FIG. 6 shows the embodiment shown in FIG. 1 more specifically. A multiprobe  31  shown in FIG. 6 is an example of a self-detection type multiprobe which utilizes resistive elements as sensors and in which cantilevers  33 ,  34  and  35  are provided on a body  32 . While the cantilevers  33 ,  34  and  35  have the same length, the cantilevers  33  and  34  are formed with wide base portions  33 A and  34 A. As a result, resonance frequencies f 33 , f 34  and f 35  of the respective cantilevers  33 ,  34  and  35  are in the following relationship with each other. 
     
       
         f 33 &gt;f 34 &gt;f 35   
       
     
     Respective spring constants k 33 , k 34  and k 35  are in the following relationship with each other. 
     
       
         k 33 &gt;k 34 &gt;k 35   
       
     
     In order to electrically detect deflection of the cantilever  33 , the cantilever  33  is provided with piezoresistance layers  33 B and  33 C formed using ion implantation. The piezoresistance layers  33 B and  33 C have a configuration in which they can be connected to a detection circuit (not shown) by wires  33 D,  33 E and  33 F constituted by metal films made of aluminum or the like. 
     While a configuration for detecting deflection of the cantilever  33  has been described, the cantilevers  34  and  35  will not be described because they have similar configurations in which reference symbols  34 C through  34 F and  35 C through  35 F corresponding to the reference symbols  33 C through  33 F are shown. 
     While either separate wiring or series wiring may be used for the sensors, separate wiring is preferred in that it provides higher sensitivity. When one of the cantilevers is selected, the sensor provided on another cantilever may be used as a reference element to obtain measurement data by eliminating drifts and noises. 
     FIG. 7 shows an example of a circuit configuration for performing such measurement. In the example of a circuit configuration shown in FIG. 7, when the cantilever  33  is used for measurement, a differential amplifier DA is used to find the difference between a detection voltage Vd generated at the piezoresistance layers  33 B and  33 C and a detection voltage Vr generated at the piezoresistance layers  35 B and  35 C of the cantilever  35  which is not used for measurement. It is possible to obtain a voltage signal representing deflection of the cantilever  33  having less drifts and noises from an output DA 1  of the same. 
     FIG. 8 shows a modification of the multiprobe  31  shown in FIG. 7, and a multiprobe  31 ′ shown in FIG. 8 has a reference sensor Sr which is separately provided in a reference cantilever within the array of probes. Since the configuration of the multiprobe  31 ′ is otherwise the same as that of the multiprobe  31 , the description for the same will be omitted with parts of the multiprobe  31 ′ corresponding to those of the multiprobe  31  indicated by like reference symbols. The reference sensor Sr has the completely same configuration as that of the sensor provided on each of the cantilevers  33 ,  34  and  35  and can be fabricated simultaneously with them. 
     FIG. 9 is a block diagram showing a general configuration of a scanning probe microscope apparatus utilizing a multiprobe  31  according to the invention as described above. A sample  102  is placed on a three-dimensional sample stage  101  serving as means for controlling relative movement between the multiprobe  31  and the sample, and the multiprobe  31  is provided above the sample  102  in a face-to-face relationship. 
     Vibrations are applied to the multiprobe  31  from a vibrator serving as means for vibrating the multiprobe  31  (not shown) and, in the example shown in FIG. 9, the vibration frequency is set at the resonance frequency f 35  of the cantilever  35 , and the scanning needle D 35  of the cantilever  35  taps a surface of the sample  102  (see FIG.  6 ). 
     A measuring portion  103  applies a bias signal to the piezoresistance layers  35 B and  35 C of the multiprobe  31  and amplifies an output signal that is in accordance with displacement of the cantilever  35 . A detection signal S 1  of the multiprobe  31  detected by the measuring portion  103  is input to a non-inverting input terminal (+) of a differential amplifier  104 . 
     A reference value for the detection signal from the multiprobe  31  is input from a reference value generating portion  105  to an inverting input terminal (−) of the differential amplifier  104  such that, for example, the output of the differential amplifier  104  is set at 0 when the deflection of the cantilever  35  is 0. As described with reference to FIG. 7, the sensor of another cantilever which is not involved in the measurement may be used as the reference value generating portion  105 . 
     An error signal S 2  output by the differential amplifier  104  is input to a control portion  106 . The control portion  106  controls an actuator drive amplifier  107  such that the error signal S 2  approaches 0. An output signal from the control portion  106  is output to a CRT as a luminance signal. A scan signal generating portion  108  outputs a signal to scan the sample  102  in X- and Y-directions to the actuator drive amplifier  107 , and the CRT outputs a raster scan signal. As a result, a three-dimensional image associated with the output signal of the multiprobe  31  is displayed on the CRT. Only a general configuration of the apparatus has been described above, and the apparatus may be configured in other ways as long as the same functions and the like are maintained. 
     According to the present invention, since one of a plurality of cantilevers prepared in advance can be selectively involved in measurement only by changing the frequency of vibration, it is possible to eliminate troublesome operations such as replacing probes and breaking cantilevers. 
     Therefore, when measurement is carried out using cantilevers having different spring constants for the reason that observation data can vary if the measurement is carried out using cantilevers having different spring constants depending on the hardness and quality of the sample, there is no need for repeating the measurement from the beginning with the cantilevers on the body replaced. Instead, by preparing cantilevers having different spring constants, continuous measurement can be carried out by changing the resonance frequency to switch the cantilevers, which allows optimum measurement to be performed easily. It is therefore possible to provide a multiprobe and a scanning probe microscope which are quite easy to operate.