JPH1183874A - Scanning type probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a probe microscope equipped with a sensitive lever chip which has a self-displacement detecting function and is excellent in environment resistance. SOLUTION: This microscope is structured so that a piezo resistance layer 2 is formed at least in a fixed end part of a sensitive lever part 1b, and a displacement of a probe 1a is detected by a change in a resistance value of the piezo resistance layer 2. Thereby, the microscope is not influenced by an environment, by giving a self displacement detecting function to a sensitive lever chip 1 (probe 1a, sensitive lever part 1b), also by forming a protective film 3 only on the surface of the part where the piezo resistance layer 2 is formed on the surface of the sensitive lever part 1b and by covering the surface of the pieze resistance layer 2 with the protective film 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning probe microscope.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional configuration of an AFM (atomic force microscope) which is one of scanning probe microscopes.
The AFM includes a cantilever L having a tip with a small radius of curvature at the tip and an optical system D for detecting the displacement of the cantilever L. When the tip comes close to the surface of the sample S, sample atoms and Due to the force acting between the probe and
Utilizing the point where the cantilever L bends, the cantilever L
This is a microscope that employs a so-called optical lever method in which the optical system D detects the bending of the light.

In the AFM, in addition to the above-described displacement detection method, an attempt has been made to integrate a cantilever and a displacement detection system. As an example, there is a method in which a piezoresistive element is formed in a silicon cantilever and displacement of the cantilever is detected from a change in the resistance value (Int).
ernational Conference on Solidstate Sensors andAct
uators, 1991, Tech.dig.pp448-451). This method has advantages over the optical lever method in that the optical axis adjustment is not required and it can be used even in a vacuum.

[0004]

In the case of the optical lever system shown in FIG. 1, there is a problem that an optical system for detecting displacement is required separately from the cantilever chip, and the device becomes large. Further, when it is desired to perform measurement in a high vacuum, the detection system also needs to be arranged in the vacuum chamber, which limits the structure. Further, when the used amount of the cantilever tip increases, the tip probe becomes worn, so that the tip needs to be replaced. However, it is necessary to perform precise optical axis adjustment every time the tip is replaced.

On the other hand, in the case of a displacement detection system using a piezoresistor, the above problem can be solved. However, in this system, when the piezoresistive layer is exposed, the influence of the environment such as humidity and mobile ions is reduced. Susceptible to noise drift. In particular, in the observation of a biological sample such as a biological sample in a liquid, which has recently attracted attention as an application of the AFM observation, the problem such as noise drift becomes remarkable, and the observation becomes difficult.

The present invention has been made in view of such circumstances, and has a self-displacement detecting function of detecting the displacement of a probe and is provided with a cantilever tip having a structure that is hardly affected by a measurement environment. The purpose is to provide a microscope.

[0007]

In order to achieve the above object, a scanning probe microscope according to the present invention comprises a cantilever tip used for measurement comprising a cantilever portion and a probe formed at a free end of the lever portion. With the structure provided, a piezoresistive layer is formed at least at the fixed end of the cantilever portion,
It is configured to detect the displacement of the probe from the change in the resistance value of the piezoresistive layer, and only the surface of the portion of the cantilever portion where the piezoresistive layer is formed is covered with the protective film. It is characterized by:

According to the scanning probe microscope of the present invention having the above configuration, the surface of the piezoresistive layer is covered with the protective film, so that it is hardly affected by the environment such as humidity and mobile ions.

In the present invention, the protective film is formed only on the surface of the portion of the cantilever portion where the piezoresistive layer is formed, because the protective film is formed on the entire cantilever portion including the piezoresistive portion. This is to avoid the point that the cantilever portion is bent due to the film stress when is present.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

The scanning probe microscope of this embodiment comprises a cantilever tip having a probe, a stage for scanning the sample S, and the like, similarly to the known microscope shown in FIG.

As shown in the schematic diagram of FIG. 2, the cantilever tip 1 is a silicon tip having a cantilever portion 1b, a pedestal 1c for supporting the cantilever portion 1b, and a probe 1a provided at a free end of the cantilever portion 1b. A piezoresistive layer 2 for displacement detection (see FIG. 3) is formed near the base of the cantilever 1b.

The cantilever chip 1 is formed with a pair of electrodes 2a (see FIG. 4) which are electrically connected to the piezoresistive layer 2. The resistance of the piezoresistive layer 2 is determined by using the pair of electrodes 2a. The change can be extracted to the outside as an electric signal. The electric signal is guided to a displacement detection circuit or the like via an amplifier. In the structure shown in FIG. 2, the electrode 2b is an electrode for applying a bias.

In this embodiment, as shown in FIG. 3, only the surface of the fixed end on which the piezoresistive layer 2 is formed is covered with the protective film 3 as shown in FIG. The feature is that the structure is less affected by the environment such as humidity and mobile ions.

In this embodiment, for the purpose of improving the temperature characteristics of the element, as shown in FIG. 2, the piezoresistive layer 2 'for temperature compensation is subjected to a stress exerted by the bending of the cantilever portion 1b. It is formed in a position that does not exist.

Next, the cantilever chip 1 having the structure shown in FIG.
4 are shown in FIGS. 4 (1) to 4 (8).

(1) First, an n-type SOI wafer 11 (Silicon
con on Insulator (a wafer having an oxide film layer 11a in silicon). Here, the thickness of the active layer on the surface side is about 15 μm.

(2) An oxide film 12 is formed on the surface of the wafer 11 and is patterned into a circular shape by using a photolithography technique. The silicon film is etched by using the patterned oxide film 12 as a mask to form a probe 1a. To form Here, dry etching (RIE; reactive ion etching) is used, but wet etching using KOH or the like may be used, or a combination thereof may be used.

(3) Thermal oxidation is performed to form an oxide film (protective film) 13 on the surface of the wafer 11. (4) A portion to be a fixed end of the cantilever portion 1b (FIG. 2)
Then, boron ions are selectively implanted to form a piezoresistive layer 2 (a piezoresistive layer 2 'for temperature compensation is not shown).

(5) The n ⁺ layer 20 is formed by performing phosphorus ion implantation and annealing for substrate contact.

(6) After forming a contact hole in a part of the oxide film 13, an Al film for an electrode is formed by sputtering or the like, the Al film is patterned, and then sintering is performed to form a piezoresistive layer. An electrode 2a conducting to the second electrode 2;
An electrode 2b conducting to the n ⁺ layer 20 is formed.

(7) The silicon on the oxide film layer 11a is etched into a cantilever chip shape, and the oxide film 13 on the surface of the cantilever portion 1b excluding the surface of the fixed end on which the piezoresistive layer 2 is formed. Is removed.

(8) With only the portion of the back surface of the wafer 11 to be the pedestal 1c of the cantilever chip 1 covered with an oxide film (not shown), Si The etching and the etching of the oxide film layer 11a using BHF (buffered hydrofluoric acid) are performed.

The chip having the structure shown in FIG.
That is, a cantilever chip 1 having a structure in which a piezoresistive layer 2 for detecting displacement is formed at the fixed end of the cantilever portion 1b and the surface of the piezoresistive layer 2 is covered with a protective film 3.
Is completed.

In the cantilever tip 1 manufactured as described above, when the probe 1a receives an attractive force or a repulsive force from surface atoms of the sample S, the cantilever portion 1b bends.
At this time, the resistance value of the piezoresistive layer 2 formed on the cantilever portion 1b changes in accordance with the stress. Therefore, if a change in the resistance value of the piezoresistive layer 2 is detected by an external displacement detector circuit, information relating to the displacement of the probe 1a can be obtained. Thus, the surface shape of the sample S can be obtained by sampling the sample S and the probe 1a of the cantilever tip 1 while relatively moving them.

Here, in the embodiment of the present invention,
Since the protective film 3 covering the piezoresistive layer 2 is formed, in the process of forming the protective film 3, an oxide film is formed on the probe 1 a (step (3) in FIG. 4) and a subsequent oxide film is formed. Since the respective processes of removal (step (7) in FIG. 4) are performed, the probe 1a
Has the effect of sharpening the tip.

In the manufacturing method shown in FIG.
Although a wafer was used as a material, the present invention is not limited to this. For example, a wafer obtained by epitaxially growing an n-type layer on a p-type silicon substrate, or a wafer formed by diffusing an n-type layer on a surface layer of a p-type silicon substrate can be used. It may be used as a material for chip production. In this case, at the time of silicon etching performed in the step (8) of FIG. 4, an electrochemical etching stop technique (IEEE, Transactions on Electron Devic) is used.
e vol. 36, No. 4, 1989) to form the cantilever portion.

Although the silicon thermal oxide film is used as the protective film 3, the material and method of forming the protective film are not limited to this. For example, a silicon oxide film or a silicon nitride film formed by a CVD method may be used. Is also good.

[0029]

As described above, according to the present invention,
Since the cantilever tip has a self-displacement detection function that detects the displacement of the probe from the change in the resistance value of the piezoresistive layer formed on the cantilever part, the surface of the piezoresistive layer is covered with a protective film. Noise due to environmental influences
Drift and the like hardly occur, and stable sample observation becomes possible. Thus, a scanning probe microscope having a cantilever tip having a self-displacement detecting function can be used, for example, in an AFM.
As an application of observation, it can be applied to observation in a liquid such as a biological sample that is of interest.

According to the present invention, only the portion of the surface of the cantilever portion where the piezoresistive layer is formed is covered with the protective film, and the other portion has a structure of only the base material without the protective film. There is no problem that the cantilever is bent by the stress.

Furthermore, in the process of forming the protective film, the probe at the tip of the cantilever is subjected to a process of forming an oxide film and then removing the oxide film, so that the tip of the probe has a sharpening effect and the scanning probe An improvement in the in-plane resolution of the microscope can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a conventional structure of a scanning probe microscope (AFM).

FIG. 2 is a diagram schematically showing a structure of a cantilever chip used in the embodiment of the present invention.

FIG. 3 is an enlarged view of a portion A in FIG. 2;

FIG. 4 is an explanatory view of a method for manufacturing the cantilever chip shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 cantilever tip 1a probe 1b cantilever part 1c pedestal 2 piezoresistive layer (displacement detecting element) 2a, 2b electrode 3 protective film

Claims (1)

[Claims] 1. A cantilever tip having a probe at a free end, and a mechanism for relatively moving a tip of the tip and a sample in a two-dimensional direction, and detecting a displacement of the probe during the moving process. In the microscope for obtaining measurement information of the fine structure on the sample surface, a piezoresistive layer is formed on the cantilever tip at least at a fixed end of the cantilever portion, and the displacement of the probe is determined from a change in the resistance value of the piezoresistive layer. A scanning probe microscope configured to detect, and wherein only a surface of a portion of the cantilever portion where a piezoresistive layer is formed is covered with a protective film.