JP3805418B2 - AFM cantilever - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AFM cantilever used for an atomic force microscope (AFM).
[0002]
[Prior art]
Conventionally, since a scanning tunneling microscope (STM) was invented by Binning and Rohrer et al. As a device capable of observing conductive samples with atomic size order resolution, it has been used in various directions as a microscope capable of observing atomic order surface irregularities. The use of is progressing. However, in STM, the observable sample is limited to a conductive sample.
[0003]
Therefore, an atomic force microscope (AFM) is a microscope capable of observing an insulating sample, which is difficult to measure with STM, with an accuracy of atomic size order while utilizing elemental technology such as servo technology in STM. was suggested. This AFM is disclosed in, for example, Japanese Patent Laid-Open No. 62-130302 (IBM, G. Vinich, method and apparatus for forming an image of a sample surface).
[0004]
The structure of AFM is similar to STM and is positioned as one of the scanning probe microscopes. In AFM, a cantilever beam (cantilever) having a sharp protrusion (probe part) at the free end is brought close to and opposed to the sample, and the interaction force acting between the atom at the tip of the probe part and the sample atom By scanning the sample in the XY direction while measuring the movement of the cantilever beam displaced by the electric or optical, and relatively changing the positional relationship with the probe portion of the cantilever beam, It is possible to capture the unevenness information of a sample in three dimensions on the atomic size order.
[0005]
As a cantilever tip for a scanning probe microscope such as an AFM having such a structure, T.W. R. Since Albrecht et al. Proposed a cantilever made of a silicon oxide film that can be fabricated by applying a semiconductor IC manufacturing process [Thomas R. Albrecht and Calvin F. Quate: Atomic resolution imaging of a nonconductor Atomforce Microscopy J. Appl. Phy. 62 (1987) 2599], and it is possible to fabricate with high accuracy of micron order and excellent reproducibility. Moreover, such a cantilever chip can be manufactured by a batch process, and cost reduction is realized. Therefore, at present, cantilever chips manufactured by applying a semiconductor IC manufacturing process have become mainstream.
[0006]
On the other hand, in recent years, in order to further integrate semiconductor integrated circuits, attempts have been made to form trench holes in a silicon substrate and to form capacitors and transistors therein. At this time, since the shape of the trench hole and the roughness of the sidewall surface influence the characteristics of the capacitor or transistor, a method for simply evaluating the shape and the roughness of the surface after forming the trench hole is desired. A probe forming method effective for performing such evaluation by AFM is described in Thomas. Bayer et al. Have proposed (Japanese Patent Laid-Open No. 3-104136, IBM, Thomas Bayer et al., A method of forming ultrafine silicon taps).
[0007]
Next, a method for forming the probe will be described with reference to FIG. First, as shown in FIG. 7A, a silicon substrate 701 having a silicon oxide film 702 formed thereon as a start substrate is used, and a generally circular pattern for forming a probe is transferred to the silicon oxide film 702. By using this silicon oxide film 702 as a mask, the silicon substrate 701 is subjected to an anisotropic RIE process to form a columnar protrusion shaft 703. Next, as shown in FIG. 7B, the side wall of the columnar projection shaft 703 is shallow and isotropically etched to reduce the projection shaft diameter and to form a conical base 703a below the projection shaft. As a result, the mechanical stability of the projection shaft 703 is improved. Next, as shown in FIG. 7C, anisotropic wet etching is performed to form a negative cross-sectional shape immediately below the mask made of the silicon oxide film 702. Finally, by removing the mask made of the silicon oxide film 702, as shown in FIG. 7D, a probe 704 having a shape whose tip is spread outward is formed.
[0008]
By using a probe having a shape whose tip is expanded outward in this way, the shape of a trench hole having a negative gradient angle and the roughness of the side wall thereof can be measured.
[0009]
[Problems to be solved by the invention]
Thomas mentioned above. The cantilever proposed by Bayer et al. Is made of silicon, as can be seen from the manufacturing method. In the AFM measurement of the sample side wall, the measurement is performed by bringing the probe into contact with the sample side wall, so that the softer the lever characteristic, the higher the measurement sensitivity. However, in a silicon cantilever, it is extremely difficult to stably produce a thin lever film with a thickness of 1 μm or less, and it is difficult to soften the lever characteristics, resulting in a decrease in measurement sensitivity. In addition, the silicon probe has a problem in that measurement reproducibility cannot be obtained because of excessive wear in contact measurement. Furthermore, since the probe is charged by static electricity or the like, there is a problem that measurement reproducibility cannot be achieved.
[0010]
The present invention has been made to solve the above-mentioned problems in the conventional AFM cantilevers, and an object of the present invention is to provide an AFM cantilever having high measurement resolution and high strength . An object of the present invention is to provide an AFM cantilever having high strength and improved side wall observation sensitivity suitable for trench hole side wall evaluation. An object of the present invention is to provide an AFM cantilever having a probe portion having a shape frequently used for normal AFM measurement, having high strength and improved measurement resolution.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the invention according to claim 1 is characterized in that a silicon probe part is disposed in the vicinity of the free end of the silicon nitride film cantilever extending from the support part, and at least the silicon probe part is provided. In the AFM cantilever configured so that the lower side surface is covered with a silicon nitride film formed integrally with the silicon nitride film forming the cantilever, the silicon covered with the silicon nitride film forming the cantilever The AFM cantilever is configured so that a constricted portion is formed on the lower side surface of the probe-making portion . With this configuration, it is possible to easily constitute the cantilever with a thin silicon nitride film, it is possible to improve the measurement resolution, the probe portion prevents exit the cantilevers, the intensity on a large it is possible.
[0012]
According to a second aspect of the invention, the AFM cantilever according to claim 1, wherein the silicon probe portion has a shape tip of its is spread outward, so that the silicon to form the tip portion is exposed It is composed of By configuring in this way, it is possible to improve the side wall observation sensitivity of trench holes and the like while maintaining the strength . According to a third aspect of the present invention, in the AFM cantilever according to the first aspect, the probe portion is configured to have a conical shape. By configuring in this way, the measurement resolution can be improved while maintaining the strength by applying the configuration of the first aspect of the invention to an AFM cantilever having a probe portion having a shape frequently used for normal AFM measurement. Can do.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
Next, embodiments of the invention will be described. 1A and 1B are views for explaining the configuration of a first embodiment of an AFM cantilever according to the present invention. FIG. 1A is a cross-sectional view thereof, and FIG. 1B is a perspective view thereof. The AFM cantilever 100 according to the embodiment of the present invention includes a probe portion 101 made of single crystal silicon, a cantilever 102 made of a silicon nitride film, and a support portion 103 made of single crystal silicon. The cantilever 102 is disposed in the vicinity of the free end, its tip extends outward, and its lower side surface is covered with a silicon nitride film 104 that forms the cantilever 102. In the figure, reference numeral 105 denotes a silicon oxide film interposed between the cantilever 102 and the support portion 103. The reason why the lower side surface of the probe unit 101 is covered with the silicon nitride film 104 forming the cantilever 102 is to firmly attach the probe unit 101 to the cantilever 102.
[0014]
Next, a method of manufacturing the AFM cantilever according to the first embodiment configured as described above will be described with reference to the manufacturing process cross-sectional views of FIGS. First, as shown in FIG. 2A, in order to manufacture this cantilever, a substrate in which two (100) silicon substrates are bonded via a silicon oxide film as a start substrate, that is, bonded SOI (Silicon On Insulator). ) Prepare the substrate 211. One of the thicknesses of the two substrates bonded together is, for example, 15 μm, and this is used as a substrate for forming the probe portion. The other is, for example, 500 μm, which is used to form the support. Further, the thickness of the intermediate silicon oxide film is, for example, 1 μm. Then, after forming a silicon oxide film of 1 μm, for example, on the surface of the SOI substrate 211, a silicon oxide film mask pattern 212 for forming a probe portion is formed at a predetermined location where the probe portion on the substrate surface is to be formed by a normal lithography process. A mask pattern 213 for forming a support portion is formed on the back surface of the substrate.
[0015]
Next, as shown in FIG. 2B, by using the silicon oxide film mask pattern 212 as a mask, the surface of the SOI substrate 211 is etched until the silicon oxide film of the intermediate layer is exposed. Form. At this time, by appropriately selecting the etching conditions, the tip of the probe portion is expanded outward.
[0016]
Next, as shown in FIG. 2C, after the silicon oxide film mask pattern 212 is peeled off, a silicon nitride film 214 for forming a cantilever is formed on the entire surface. As the silicon nitride film 214, a film having a silicon content higher than that of a silicon / nitrogen composition of 3: 4, which is often used in a semiconductor element, is used. Thereby, since a thermal expansion coefficient approaches silicon, when peeling a board | substrate silicon | silicone and forming a cantilever, it can prevent that a cantilever warps. Next, a photoresist 215 serving as a mask when the silicon nitride film 214 is processed into a cantilever shape is formed. At this time, the film thickness of the photoresist 215 is selected so that the tip of the probe portion 201 is exposed.
[0017]
Next, the silicon nitride film 214 is etched using the photoresist 215 as a mask to process it into a cantilever pattern and to expose silicon at the tip of the probe portion. Next, as shown in FIG. 2D, a silicon oxide film 216 is formed at the tip of the probe portion where the silicon is exposed by performing a thermal oxidation process. As a result, the tip edge of the probe portion 201 is sharpened, the measurement resolution is improved, and the probe portion can be protected when the substrate is etched to form a cantilever. Next, as shown in FIG. 2 (E), a probe portion having a lower side surface covered with a silicon nitride film 206 is etched from the back surface of the substrate and finally the oxide film is removed by etching with a hydrofluoric acid aqueous solution. An AFM cantilever having the same configuration as that of the first embodiment shown in FIG. Reference numeral 205 denotes a silicon oxide film.
[0018]
In the AFM cantilever of the first embodiment, the probe portion and the cantilever are fixed in such a manner that the lower side surface of the probe portion is covered with a silicon nitride film that forms the cantilever. In the case of this configuration, there is a possibility that the probe part may come off the cantilever during use. Therefore, by adopting a configuration in which the constricted portion is formed on the lower side surface of the probe portion, the probe portion does not fall out from the cantilever during use, and the use strength can be increased.
[0019]
Next, an example of a method for manufacturing an AFM cantilever in which a constricted portion is formed on the lower side surface of the probe portion will be described with reference to FIGS. First, after forming a silicon projection to be the probe portion 301 by the same manufacturing method as shown in FIG. 2B, the probe portion 301 is placed on the upper portion of the probe portion 301 as shown in FIG. A resist pattern 317 is formed so that most of it is hidden and the proximal end portion of the probe portion 301 is exposed. By applying isotropic silicon etching to the probe portion 301 using the resist pattern 317 as a mask, a constricted portion 318 can be formed on the lower side surface of the probe portion as shown in FIG. Thereafter, as shown in FIG. 3C, a silicon nitride film 314 for forming a cantilever is formed on the entire surface, and is embedded in the constricted portion 318. As a result, an AFM cantilever in which the probe portion 301 is firmly fixed to the cantilever is obtained.
[0020]
[Second Embodiment]
Next, a second embodiment of the AFM cantilever according to the present invention will be described with reference to FIG. In this embodiment, as shown in FIG. 4, the silicon at the tip of the probe 401 is not exposed, and the silicon nitride film 404 forming the cantilever 402 is formed so as to cover the entire probe. In this respect, the configuration is different from that of the first embodiment. In FIG. 4, 403 is a support portion and 405 is a silicon oxide film.
[0021]
By configuring in this way, the tip of the probe part in contact with the sample surface is covered with a silicon nitride film harder than silicon, so that the AFM cantilever can be measured with less wear and with good reproducibility. Is obtained.
[0022]
[Third Embodiment]
Next, a third embodiment of the AFM cantilever according to the present invention will be described with reference to FIG. The AFM cantilever of this embodiment is an AFM cantilever having the same configuration as that of the first embodiment described above, and further has a Si ₃ N ₄ film, a DLC (diamond-like carbon) film, a SiC on the surface of the probe portion 501. A hard film 519 such as a film is formed thin, and the tip of the probe portion is covered with a hard film. In FIG. 5, 502 is a cantilever, 503 is a support portion, and 505 is a silicon oxide film.
[0023]
With this configuration, the probe portion can be covered with a film harder than the silicon nitride film having a high silicon content forming the cantilever. Therefore, the probe is further improved than the one shown in the second embodiment. The wear of the needle part is suppressed, and the measurement reproducibility is improved. Further, since the hard film can be formed thinly, deterioration of the sharpness of the tip edge due to covering the probe portion can be reduced, and higher measurement resolution than that shown in the second embodiment can be expected.
[0024]
[Fourth Embodiment]
Next, a fourth embodiment of the AFM cantilever according to the present invention will be described with reference to FIG. In the AFM cantilever of this embodiment, after forming a silicon protrusion to be the probe portion 601 by the same process as that described in the first embodiment, phosphorus or boron is formed on the silicon protrusion. Impurities are diffused at a high concentration, and then a cantilever 602 is formed in the same manner as in the first embodiment. Finally, a metal film 620 such as Au or Al is deposited on the back surface of the cantilever 602 and the support portion 603 by vapor deposition or the like. Thus, the AFM cantilever of the present embodiment can be obtained. Reference numeral 605 denotes a silicon oxide film.
[0025]
With this configuration, the probe 601 becomes conductive, and the metal film 620 formed on the back surface of the cantilever 602 and the probe 601 are electrically connected, so that the end of the cantilever support 603 is grounded. By doing so, it becomes possible to ground the potential at the tip of the probe portion. As a result, it is possible to prevent a decrease in measurement reproducibility due to charging of the probe portion due to the influence of static electricity or the like.
[0026]
In each of the above embodiments, an AFM cantilever having a probe portion with a tip extending outwardly, which is suitable for measuring the trench shape and the side wall roughness, has been described. Of course, the above-described configuration can also be applied to an AFM cantilever having a probe portion with a sharply pointed tip that is frequently used for measurement.
[0027]
【The invention's effect】
As described above based on the embodiments, according to the present invention, the cantilever is made of a silicon nitride film, and at least the lower side surface of the silicon probe portion is formed integrally with the silicon nitride film forming the cantilever. In addition, since the constricted portion is formed on the lower side surface of the probe portion, the measurement resolution can be improved and the probe portion can be firmly attached to the cantilever .
[Brief description of the drawings]
FIG. 1 is a transverse sectional view and a perspective view showing a first embodiment of an AFM cantilever according to the present invention.
FIG. 2 is a diagram showing a manufacturing process for explaining the manufacturing method of the first embodiment shown in FIG. 1;
FIG. 3 is a diagram showing a manufacturing process for explaining a manufacturing method according to a modification of the first embodiment.
FIG. 4 is a cross-sectional view showing a second embodiment of the present invention.
FIG. 5 is a cross-sectional view showing a third embodiment of the present invention.
FIG. 6 is a cross-sectional view showing a fourth embodiment of the present invention.
FIG. 7 is a diagram illustrating a manufacturing process for explaining a method for manufacturing a probe portion of a conventional AFM cantilever.
[Explanation of symbols]
100 AFM cantilever
101,201,301,401,501,601 Probe unit
102,202,402,502,602 Cantilever
103,203,403,503,603 Support part
104,204,404 Silicon nitride film
105,205,405,505,605 Silicon oxide film
211 SIO board
212 Silicon oxide film mask pattern for probe formation
213 Silicon oxide mask pattern for supporting part formation
214 Silicon nitride film
215 photoresist
216 Silicon oxide film
317 resist pattern
318 Constriction
519 Hard film
620 Metal film

Claims (3)

A silicon probe portion is disposed in the vicinity of the free end of the silicon nitride film cantilever extending from the support portion, and at least the lower side surface of the silicon probe portion is formed integrally with the silicon nitride film forming the cantilever. In the AFM cantilever configured to be covered with the silicon nitride film, a constricted portion is formed on the lower side surface of the silicon probe portion covered with the silicon nitride film forming the cantilever. AFM cantilever, characterized in that there.   2. The AFM cantilever according to claim 1, wherein the tip portion of the silicon has a shape in which a tip end portion is expanded outward, and silicon forming the tip portion is exposed. 3.   The AFM cantilever according to claim 1, wherein the tip portion of the silicon probe has a cone-shaped tip.

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