JPH09203738A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cantilever chip that has the function of detecting its own displacement and is less likely to be affected by measuring environments by making a piezoresistance layer that is formed on a cantilever part into an embedded resistance layer obtained by injection of high-energy ions. SOLUTION: A cantilever chip 1 is a silicon chip, consisting of a cantilever part 1b, a base 1c, and a probe 1a, with an embedded piezoresistance layer 2 formed near the root of the lever part 1b by injection of high-energy ions. When the probe 1a is exerted with attracting or repelling forces from the surfaces of atoms in the sample S, the lever part 1b is deflected, and the resistance value 2 is changed in resistance value according to its stress. This change in resistance value is detected, whereby information about the displacement of the lever part 1b, i.e., the probe 1a, can be obtained. The resistance layer 2 is an embedded dopant layer obtained by injection of high-energy ions, and can be formed with the conducting die of a substrate surface layer left on its upper layer. Therefore, the cantilever chip that is less likely to be affected by environmental changes because of surface-layer protection can be obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a scanning probe microscope.

[0002]

2. Description of the Related Art FIG. 4 shows the configuration of an AFM (atomic attraction microscope) which is one of scanning probe microscopes. This A
The FM is composed of 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. This is a microscope that employs a so-called optical lever method that utilizes the point where the cantilever bends due to the force acting between the needle and the optical system D to detect the bending of the cantilever.

In addition to the displacement detection method described above, it has been attempted to integrate a cantilever and a displacement detection system in this type of microscope, and as an example of a cantilever chip having a self-displacement detection function, There is a method in which a piezoresistive element is formed in a silicon cantilever, and the displacement of the cantilever is detected from the change in the resistance value.
national Conference on Solidstate Sensors and Actu
ators, 1991, Tech.dig.pp448-451).

[0004]

By the way, the structure shown in FIG. 4 has a problem that an optical system for displacement detection is required in addition to the cantilever chip, and the device becomes large in size.
Further, when it is desired to perform the measurement in a high vacuum, the detection system also needs to be arranged in the vacuum chamber, which limits the configuration.

On the other hand, when a cantilever chip in which a piezoresistive element is formed in a cantilever portion is used, the resistance of the piezoresistive element is not limited by the above-described configuration, but the resistance of the piezoresistive element is measured in an environment (eg, humidity). And there is a problem that a measurement error occurs. Especially,
In in-liquid observation of a biological sample or the like, which has recently attracted attention as an application of AFM observation, the variation in resistance value becomes remarkable, which makes observation difficult.

The present invention has been made in view of such circumstances, and has a scanning probe microscope having a cantilever tip which has a self-displacement detecting function for detecting the displacement of a probe and is not easily affected by the measurement environment. The purpose is to provide.

[0007]

In order to achieve the above object, the scanning probe microscope of the present invention is such that the cantilever tip used for measurement is made of a semiconductor material, and the resistance of the piezoresistive layer formed in the cantilever portion is The piezoresistive layer is configured to use the value change as a displacement detection signal of the probe, and is characterized by being a buried resistive layer formed by high energy ion implantation.

The high-energy ion implantation referred to in the present invention means implanting ions with energy capable of filling a dopant layer having a conductivity type different from that of the substrate while leaving the conductivity type of the substrate surface layer. Point to.

[0009]

In FIG. 1, for example, the probe 1a receives an attractive force or a repulsive force from the atoms on the sample surface to cause the cantilever portion 1b.
When the bending occurs, the embedded piezoresistive layer 2 formed on the cantilever portion 1b undergoes a change in resistance value according to the stress. Therefore, if a change in the resistance value of the embedded piezoresistive layer 2 is detected by an external circuit, the cantilever portion 1 is detected from the detected value.
The deflection of b, that is, the displacement of the probe 1a can be known.

Here, since the buried dopant layer formed by the high energy ion implantation can be formed in a state where the conductivity type of the substrate surface layer is left as an upper layer, the buried dopant layer is protected from the outside by the surface layer and the environmental change is prevented. It has a characteristic that it is hardly affected, and therefore, the buried piezoresistive layer formed by such high energy ion implantation has excellent environmental resistance.

[0011]

FIG. 1 is a block diagram of an embodiment of the present invention. The scanning probe microscope shown in FIG. 1 is composed of a cantilever tip 1 having a self-displacement detecting function and a stage (see FIG. 4) for scanning the sample S, as in a known microscope. The structure of the cantilever tip 1 is characteristic.

That is, the cantilever tip 1 of this example
Is a cantilever portion 1b and a pedestal 1c supporting the cantilever portion 1b,
A silicon chip having a probe 1a provided at the free end of the cantilever portion 1b, and a buried piezoresistive layer 2 is formed by high-energy ion implantation near the root of the cantilever portion 1b.

Further, as shown in FIGS. 1 and 2, the cantilever chip 1 is formed with a pair of electrodes 2a electrically connected to the embedded piezoresistive layer 2.
By utilizing a, the change in the resistance value of the embedded piezoresistive layer 2 can be taken out as an electric signal to the outside. Then, the electric signal is guided to a detection circuit (not shown) or the like via the amplifier. In the structure shown in FIG. 1, the electrode 3a is a bias application electrode.

In the above structure, when the probe 1a receives an attractive force or a repulsive force from the surface atoms of the sample S, the cantilever portion 1b bends. At this time, the resistance value changes in the embedded piezoresistive layer 2 formed in the cantilever portion 1b according to the stress. Therefore, by detecting a change in the resistance value of the embedded resistance layer 2 by an external detection circuit or the like, this detected value can be used as the deflection of the cantilever portion 1b, that is, the displacement information of the probe 1a.

Next, the cantilever tip 1 having the structure shown in FIG.
The procedure for producing the above will be described below with reference to steps (1) to (5) shown in FIG. (1) First, SOI wafer 11 (Silicon on Insulator;
A wafer having an oxide film layer 11a in silicon) is used as a material. Here, the thickness of the active layer on the front surface side is about 15 μm.

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

(3) After forming the passivation film (oxide film) 11b on the surface of the wafer 11, the n ⁺ layer 3 for the substrate contact is formed by phosphorus ion implantation, and then the p ⁺ layer 2b for the resistance layer contact. Are formed by boron ion implantation (low energy ion implantation; for example, 30 KeV). After that, the buried piezoresistive layer 2 is formed by implanting boron ions. At this time, the implantation energy of boron is such that the buried resistance layer can be formed while leaving the conductivity type of the wafer 11 as a substrate (for example, 1 M).
eV).

(4) Annealing is performed to activate the ion-implanted layer, and then the buried piezoresistive layer 2 and n ⁺ layer 3 are formed.
After forming a contact hole to the electrodes, electrodes 2a and 3a which are electrically connected to the respective layers are formed.

(5) An oxide film (not shown) is formed only on the back surface side of the wafer 11 to be the base 1c of the cantilever chip 1.
In the state covered with, the back surface of the wafer 11 is etched to form the cantilever portion 1b.

Through the above steps, the chip having the structure shown in FIG.
That is, the cantilever chip 1 having a structure in which the embedded piezoresistive layer 2 for displacement detection is formed in the cantilever portion 1b is completed.

In the above embodiments, the SOI wafer is used as the material, but the material is not limited to this and, for example, p
A wafer in which an n-type layer is epitaxially grown on a type silicon substrate or a wafer in which an n-type layer is diffused on a surface layer of a p-type silicon substrate may be used as a material for chip fabrication. In this case, electrochemical etching stop technology (IEEE, Transactions on Electron Devices vol.
36, No. 4, 1989) to form the cantilever portion.

In the present invention, the material of the cantilever tip is not limited to silicon, and any other semiconductor material may be used as long as it can form the buried piezoresistive layer.

[0023]

As described above, according to the scanning probe microscope of the present invention, the cantilever tip detects the displacement of the probe from the change in the resistance value of the piezoresistive layer formed in the cantilever portion. Since the structure is functional and the piezoresistive layer is a buried resistive layer formed by high-energy ion implantation, stable sample observation is possible because it is less susceptible to changes in the measurement environment. This makes it possible to apply a scanning probe microscope equipped with a cantilever tip having a self-displacement detection function to in-liquid observation of a biological sample or the like, which is attracting attention as an application of AFM observation.

[Brief description of drawings]

FIG. 1 is a structural diagram of an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a structure of a buried piezoresistive layer 2 and an electrode 2a according to the embodiment.

FIG. 3 is a diagram illustrating a method of manufacturing the cantilever tip 1 shown in FIG.

FIG. 4 is a diagram showing a structural example of a scanning probe microscope (AFM).

[Explanation of symbols]

 1 cantilever tip 1a probe 1b cantilever part 1c pedestal 2 embedded piezoresistive layer 2a electrode

Claims (1)

[Claims] 1. A cantilever tip having a probe, and a stage for scanning a sample in a two-dimensional direction with respect to the probe,
In a microscope that detects the displacement of the probe in the scanning process and obtains measurement information of the fine structure of the sample surface, the cantilever tip is made of a semiconductor material, and the change in resistance of the piezoresistive layer formed on the cantilever part is searched A scanning probe microscope, which is configured to be used as a needle displacement detection signal, and whose piezoresistive layer is a buried resistive layer formed by high energy ion implantation.