Cantilever Probe and Scanning Type Probe Microscope Utilizing the Cantilever Probe

The present invention relates to a cantilever probe and a method of manufacturing the same, and more particularly to a cantilever probe and a method of manufacturing the same suitable for a scanning type probe microscope represented by the AFM (Atomic Force Microscope). Further, to describe more specifically, the present invention relates to a cantilever probe and a method of manufacturing the same in which a probe approaching the surface of a sample to be scanned thereby is provided at a free edge of the cantilever and a beam section thereof is deflected by force generated between the probe and the surface of the sample. Also, the present invention relates to observation, when a surface of a sample existing in a liquid is to be observed, of the surface of the sample with an optical lever reflecting section of the cantilever probe kept above the liquid. The present invention also relates to a scanning type probe microscope utilizing the cantilever probe.

A cantilever with a probe provided at a free edge of a beam section thereof supported in a cantilever form has been used as a scanning probe in a scanning type atomic force microscope (AFM). In the cantilever probe having the configuration as described above, when a surface of a sample is scanned with the probe, an attractive force or a repulsive force according to an interatomic force is generated between the sample surface and the probe, so that a form of the sample surface can be measured by detecting the interatomic force as a deflection rate of the cantilever.

A conventional type cantilever probe for an AFM is disclosed in, for instance, Japanese Patent Laid-Open Publication No. HEI 5-196458, in which the cantilever probe 30 has a linear form as a whole as shown in FIG. 5A and both a free edge 30b at which a probe 1 is formed and a fixed edge 30c fixed to a main body of a microscope are present on an extension line of a beam section 30a of the cantilever. However, when the linear cantilever 30 as described above is used for a scanning probe, if the cantilever is arranged in a posture that the beam section 30a is parallel to the surface of a sample, the beam section 30a may contact the surface of the sample if the sample has a largely wavy surface, whereby the probe 1 can not accurately trace the surface of the sample. For this reason, the cantilever probe 30 based on the conventional technology was attached to the main body thereof at an angle, as shown in FIG. 5B, toward the surface of a sample so that the probe 1 can accurately trace the surface thereof without contacting of the beam section 30a with the sample 20 even if the sample has a largely wavy surface.

Also, when a sample in a liquid is to be measured with the conventional type AFM, an entire cantilever probe is required to be sunk in the liquid and a lever section as a reflecting surface of an optical lever is also in the liquid, which makes it difficult to adjust a position of a laser, or a reflecting position is changed due to its refraction, absorption, or change in a liquid surface, so that reflection intensity becomes weaker or accurate measurement can not be carried out.

As described above, when the cantilever probe 30 is attached at an angle toward a surface of a sample, the probe 1 approaches the surface of the sample also at an angle toward it. FIG. 6 is a simulated view showing an interatomic force when the probe 1 approaches the surface thereof at an angle toward it, and it is clear that the interatomic force does not uniformly apply to to the probe 1 in the posture shown in the figure. For this reason, a deflection rate of the cantilever probe 30 cannot accurately represent a distance between the probe 1 and the sample 20, so that the sensitivity is reduced and a measurement error becomes larger. Also, when a sample in a liquid is to be measured, as the entire cantilever probe is sunk in the liquid, a laser for detecting an optical lever is reflected on a liquid surface or absorbed by the liquid, and also reflection intensity of a laser drops or a reflecting position is displaced, which makes it impossible to perform correct or high sensitivity detection.

The present invention was made for solving the problems relating to the conventional technology, and it is an object of the prevent invention to provide a cantilever probe and a method of manufacturing the same in which, even if a probe formed at a free edge vertically approaches a surface of a sample to be scanned thereby, the probe can accurately trace the surface thereof with the main body of the cantilever probe not contacting the surface thereof. Further, it is another object of the present invention to provide a cantilever probe and a method of manufacturing the same in which accurate observation of a sample in a liquid can be performed, when a sample in a liquid is to be observed, because a laser reflecting surface of the cantilever does not sink in the liquid. Another object of the present invention is to provide a scanning type probe microscope utilizing the cantilever probe.

To achieve the objects described above, in the present invention, the following countermeasures are taken in a cantilever probe with a probe provided at a free edge of a beam section supported in a cantilever form and in a method of manufacturing the same.

(1) In the present invention, a bending section is provided in at least one position between a fixed edge and a free edge of the beam section so that the beam section is inclined by a prespecified angle toward a surface of a sample in a state where the probe is close to the surface thereof in the vertical direction.

(2) The method according to the present invention comprises a step of forming a pair of protection coats in one edge of a surface as well as in the other edge of the rear surface of a semiconductor substrate respectively with a specified gap provided therebetween so that projections from both of the sections are not superimposed on each other, a step of executing anisotropic etching to the silicon substrate from the top surface as well as from the rear surface thereof to a specified depth using the protection coat as a mask to form a non-linear cantilever comprising two supporting sections remained under the pair of protection coats and a beam section remained in the gap area so as to connect the supporting sections to each other therethrough, a step of forming a protection coat on the surface of one of the supporting sections, and a step of forming a probe by under-cutting the surface of the supporting section under the protection coat by subjecting it to isotropic etching.

(3) The method according to the present invention comprises a step of subjecting a surface of a silicon substrate to anisotropic etching to form a concave form with the bottom of the concave section formed into a lever section of the bent cantilever, a step of setting a gap between the cantilever and the peripheral section to some .mu.m, and a step of forming a probe at a rear surface of the lever section by subjecting it to isotropic etching.

With the cantilever having the configuration (1) as described above, even if the probe has vertically approached a surface of a sample, contact between the main body of the cantilever and the surface of the sample can be prevented, which allows the probe to accurately trace the surface thereof. With the method of manufacturing the cantilever according to the configuration (2) and the configuration (3) as described above, a non-linear cantilever probe having a bending section(s) can be formed only by chemical etching steps without requiring complicated polishing steps which are required in mechanical processing.

With the cantilever probe according to the configuration (3), as an entire cantilever probe is not required to be sunk in a liquid when a sample in the liquid is to be observed, accurate observation of a sample in a liquid can be performed because attenuation of a laser for detecting a position due to reflection on the surface of the liquid or absorption thereby does not occur or displacement of a laser does not also occur more than the displacement due to interaction between the probe and the sample due to its irregular reflection.

FIG. 1 is a side view of a cantilever probe according to one embodiment of the present invention.

FIG. 2 is a simulated view showing actions of an interatomic force when the probe has vertically approached the surface of the sample.

FIGS. 3A-3C are a view (Part one) showing a method of manufacturing a non-linear cantilever probe according to one embodiment of the present invention.

FIGS. 4A-4B are a view (Part two) showing a method of manufacturing a non-linear cantilever probe according to one embodiment of the present invention.

FIGS. 5A-5B are a view showing a structure of the linear cantilever probe based on the conventional technology and a usage thereof.

FIG. 6 is a view for explaining the problems of the linear cantilever probe based on the conventional technology.

FIG. 7A-7B are a side view and a plane view of a cantilever probe for observation in a liquid according to one embodiment of the present invention.

Detailed description is made hereinafter for the present invention with reference to the drawings. FIG. 1 is a side view of a cantilever probe according to one embodiment of the present invention, and the same reference numerals are assigned to the sections identical or corresponding to those in FIG. 1.

A cantilever probe 10 according to the present invention is constructed by subjecting a silicon substrate to etching, and has three areas with bending sections 51 and 52 each as a boundary therebetween respectively such as a supporting section 10b in the side of a free edge, a beam section 10a, and a supporting section 10c in the side of a fixed edge. A probe 1 is formed in the free edge side supporting section 10b and the fixed edge side supporting section 10c is fixed to a main body of a microscope. An angle between free edge side supporting section 10b and the beam section 10a is around 55.7.degree. at the bending section 51, and an angle between the beam section 10a and the fixed edge side supporting section 10c is around 124.30.degree. at the bending section 52. The free edge side supporting section 10b and the fixed edge side supporting section 10c are not present on the same plane but are parallel to each other, and the <100> plane is exposed on each surface of the supporting sections. Also, the <111> plane is exposed on the surface of the beam section 10a. With the non-linear cantilever probe as described above, the probe 1 can vertically approach a surface of a sample with the beam section 10a not contacting the surface thereof even if the sample has a comparatively large wavy surface. FIG. 2 is a simulated view showing actions of interatomic force when the probe 1 has vertically approached the surface of the sample, and the interatomic force is uniformly applied to the probe 1 in the posture shown in the figure, so that a deflection rate of the cantilever 30 can accurately represent a distance between the probe 1 and the sample 20.

FIG. 3A-3C and FIG. 4A-4B are cross-sectional views each showing a method of manufacturing the non-linear cantilever probe having two bending sections as described above, and the same reference numerals are also assigned to sections identical or corresponding to those in the previous figures. At first, masks 61, 62 such as an oxide film are formed in one edge of the top surface as well as in the other edge of the rear surface of the silicon substrate 3 which is a <100> plane respectively (Refer to FIG. 3A). The masks 61, 62 are arranged with a specified gap d provided therebetween so that projections from both of the sections are not superimposed on each other. The gap d in this case is decided according to a crystal structure of a material of the substrate (silicon in this embodiment), a thickness of the substrate, and a thickness of a section as a beam section 30a or the like.

Then, the top surface of the silicon substrate 3 is subjected to anisotropic wet etching as far as a specified depth using the mask 61 as a mask (Refer to FIG. 3B). As a solvent for etching, a 40 weight percent aqueous solution of potassium hydroxide (KOH) can be used at a temperature in a range from 60.degree. C. to 80.degree. C. and a 20 weight percent aqueous solution of tetramethylammonium hydroxide (TMAH) at a temperature in a range from 80.degree. C. to 90.degree. C. or the like. In those types of solvent for etching, the <100> plane is subjected to etching much quicker than the <111> plane, so that the mask 61 is practically not affected by etching. Accordingly, this anisotropic etching is practically stopped at the <111> plane with the edge section of the mask 61 as a reference, and the <111> plane is exposed in a gap area which is the beam section 30a.

When a rear surface of the silicon substrate is also subjected to anisotropic wet etching as the top surface thereof, the <111> plane with the edge section of the mask 62 as a reference is exposed in the gap area (Refer to FIG. 3C). When the silicon substrate 3 is used as in this embodiment, there is generated an angle of around 55.7.degree. (around 124.3.degree.) between the <100> plane and the <111> plane.

Then, a mask 63 is formed on the surface of the free edge side supporting section 10b (Refer to FIG. 4A), and a probe 1 is formed by under-cutting the silicon under the mask 63 with dry etching according to a height of the probe 1 (Refer to FIG. 4B). Finally, the mask 63 is removed and the cantilever 10 is completed.

With the embodiment of the present invention, a non-linear cantilever probe having amending section(s) can be formed only by wet type and/or dry type etching steps without requiring complicated polishing steps which are required in the mechanical processing.

FIGS. 7A and 7B show a cantilever probe according to the present invention having a form effective for observation of a sample in a liquid.

Observation of a surface of a sample in a liquid can be performed by sinking only the probe 1 in the liquid as shown in FIG. 7A while penetration of water due to surface tension is evaded by leaving a peripheral section 55 of the cantilever probe shown in FIG. 1 for a concave form and making a gap 55 between the cantilever probe and the peripheral section thereof as small as around 1 to 100 .mu.m.

It should be noted that description of the above embodiments assumes that a cantilever probe is formed by subjecting a silicon substrate to etching, but the present invention is not limited only to the silicon substrate, and the same type of cantilever probe can be made also by executing etching to a crystal or a gallium arsenide substrate.

With the present invention, the effects described below are achieved.

(1) In the cantilever probe according to the present invention, a bending section(s) is provided between a free edge with a probe provided thereon and a fixed edge, and a beam section is inclined by a specified angle toward a surface of a sample in a state where the probe has vertically approached the surface of the sample, so that, even if the probe has vertically approached the surface thereof, contact between the main body of the cantilever probe and the surface of the sample can be prevented, which allows the probe to accurately trace the surface of the sample.

(2) With the method of manufacturing the cantilever probe according to the present invention, a non-linear cantilever probe having a bending section(s) can be formed only by wet type and/or dry type etching steps without requiring complicated polishing steps which are required for mechanical processing.

(3) In the cantilever probe according to the present invention, an object in water can be observed simply by sinking only the probe in a liquid with the cantilever probe as a whole kept above the liquid.