JPH10132832A - Scanning probe microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a scanning probe microscope in a simple structure without using an optical system by forming a p-n junction at the fixed end part of a cantilever and detecting the displacements of a probe from changes in the current-voltage characteristics of the p-n junction part. SOLUTION: A cantilever chip 1 is provided with a cantilever part 1b, a base 1c supporting this, and a probe 1a provided for the free end of the cantilever part 1b, and an p-n junction diode 2 is formed on the fixed end part of the cantilever part 1b. In the p-n junction diode 2, p-type area is formed on a n-type layer and electrodes 3a and 3b are formed on the p-type area and n-type contact area respectively to extract signals to the outside. When the probe 1a receives attraction or repulsion from the surface atoms of a sample S, stress occurs at the flexible lever fixed end part of the cantilever part 1b to change the current-voltage characteristics of the p-n junction part of the p-n junction diode. This change is detected with scanning the sample S with the probe 1a to obtain the displacement information of the probe 1a and, consequently, information on the inside of the sample surface.

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 displacement of the cantilever L. When the tip approaches the surface of the sample S, the AFM This is a microscope that employs a so-called optical lever system in which a point at which the cantilever L is bent by a force acting between the probe and the probe is detected by the optical system D.

[0003]

However, in the case of the structure 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 a vacuum chamber, and the configuration is limited. 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.

[0004] In recent years, there has been interest in the observation of biological samples and the like in liquids as an application of AFM observation, but it is difficult to adjust the optical axis due to the difference in the refractive index of light between water and air. Therefore, in the case of the structure of FIG. 1, it is difficult to realize such an application.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a scanning probe microscope having a simple structure capable of detecting the displacement of a probe at the tip of a cantilever without using an optical system.

[0006]

In order to achieve the above object, a scanning probe microscope according to a first aspect of the present invention comprises a probe having a cantilever tip used for measurement and a cantilever portion formed at a free end of the lever portion. With a structure having a needle, a pn junction is formed at least at a fixed end of the cantilever portion,
It is characterized by being configured to detect the displacement of the probe from the change in the current-voltage characteristic of the pn junction.

In the above arrangement, when the probe receives an attractive or repulsive force from atoms on the surface of the sample and the cantilever is bent, a stress is generated at the fixed end of the lever.
The forbidden band width of the n-junction changes. Here, in the pn junction, if the forbidden band width changes due to external stress, the current-voltage characteristics of the pn junction also change according to the stress (Kiyo Takahashi; “Semiconductor Engineering” Morikita Publishing p.289-p. .290), if the change in the current-voltage characteristics is detected by an external circuit, the deflection of the cantilever portion, that is, the displacement of the probe, can be known from the detected value.

In the first aspect, a pn junction diode is formed at least at a fixed end of the cantilever portion of the cantilever tip, and a change in the current-voltage characteristic is detected as it is, so that a displacement detection signal of the probe can be obtained. Or a bipolar transistor may be formed at least at the fixed end of the cantilever, and a change in current-voltage characteristics of the base-emitter junction (pn junction) may be amplified between the emitter and collector. The detection may be performed to obtain a probe displacement detection signal.

In order to achieve the same object, the scanning probe microscope of the second invention has a structure in which a cantilever tip used for measurement is provided with a cantilever portion and a probe formed at a free end of the lever portion. A junction field-effect transistor is formed at least at a fixed end of the cantilever portion,
It is characterized by being configured to detect the displacement of the probe from the output change of the junction field effect transistor.

In the second aspect of the present invention, the output of the junction field effect transistor formed at least at the fixed end of the cantilever portion is changed by utilizing the fact that the output of the cantilever portion changes according to the stress generated by bending. Detect displacement.

That is, the sum of the external bias voltage Vo and the internal potential Vbi of the junction; VG = (Vo + Vbi) is applied to the pn junction between the gate and the channel of the junction field effect transistor formed on the cantilever chip. I have. Now, when the probe at the tip of the cantilever is displaced, stress is generated at the lever fixed end as described above, and stress is generated at the pn junction between the gate and the channel. Here, the built-in potential (Vbi) of the pn junction changes due to external stress (see Kiyoshi Takahashi; "Semiconductor Engineering", Morikita Publishing, p.290).
When a stress is applied to the n-junction, VG changes, and accordingly, the drain current changes according to the transfer characteristics inherent to the element. Therefore, if the change in the current is detected, the displacement of the probe can be known from the detected value.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an embodiment of the first invention will be described with reference to FIGS. The scanning probe microscope according to this embodiment includes a cantilever tip having a probe, a stage for scanning the sample S, and the like, similarly to the known microscope shown in FIG. Is characterized by its structure.

That is, the cantilever chip 1 of this embodiment
As shown in FIGS. 2 (a) and 2 (b), is a silicon chip provided with a cantilever 1b, a pedestal 1c for supporting the same, and a probe 1a provided at a free end of the cantilever 1b. A pn junction diode 2 for detecting displacement is formed at a fixed end of the cantilever portion 1b.

The pn junction diode 2 is shown in FIG.
As shown in the schematic diagram of (b), in a device in which a p-type region 2a is formed in an n-type layer, pn The change in the current-voltage characteristic of the junction can be taken out as an electric signal.

In the above configuration, when the probe 1a receives an attractive force or a repulsive force from surface atoms of the sample S, the cantilever portion 1b bends and a stress is generated at the lever fixed end. At this time, the current-voltage characteristics of the pn junction of the pn junction diode 2 formed at the fixed end of the cantilever 1b change according to the stress. Therefore, if a change in the current-voltage characteristic of the pn junction diode 2 is detected by an external detection circuit or the like, displacement information of the probe 1a can be obtained. With the configuration as shown in FIG. 1, if the displacement information of the probe 1a is collected while the sample S and the probe 1a of the cantilever tip are relatively moved, information in the sample plane can be obtained. .

Next, the cantilever chip 1 having the structure shown in FIG.
Will be described below with reference to steps (1) to (8) shown in FIG. (1) First, an n-type SOI wafer 11 (Silicon on Insulat
or; a wafer having an oxide film layer 11a in silicon).

(2) An oxide film is formed on the surface of the wafer 11,
This is patterned into a circle by using the photolithography technique, and the wafer 11 is etched using the patterned oxide film 12 as a mask to form the 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) Thermal oxidation is performed to form an oxide film 13 on the surface of the wafer 11. (4) Boron is selectively ion-implanted into a portion (see FIG. 2) serving as a fixed end of the cantilever portion 1b, and annealing is performed to form a p-type region 2a.

(5) An n-type contact region 2b for substrate contact is formed by selectively performing phosphorus ion implantation. (6) After forming contact holes for the p-type region 2a and the n-type contact region 2b in a part of the oxide film 13, Al for an electrode is formed by sputtering or the like, and the Al film is patterned. Electrodes 3a and 3b that are electrically connected to the respective regions 2a and 2b are formed. Thereafter, sintering is performed.

(7) The silicon on the oxide film 11a is etched into a cantilever chip shape, and the cantilever portion 1 is etched.
The oxide film of b is removed. (8) Silicon is etched from the back surface of the wafer 11 using a potassium hydroxide solution while only the portion serving as the pedestal 1c of the cantilever chip 1 on the back surface side of the wafer 11 is covered with an oxide film (not shown). After that, the oxide film 11a is etched using BHF (buffered hydrofluoric acid).

The chip having the structure shown in FIG.
That is, the cantilever chip 1 having the structure in which the pn junction diode 2 for detecting the displacement is formed at the fixed end of the cantilever portion 1b is completed.

FIG. 5 is a diagram schematically showing another configuration example of the cantilever chip used in the embodiment of the first invention. This embodiment differs from the structure of FIG. 2 in that the bipolar transistor 102 is formed at the fixed end of the cantilever 1b, and the current-voltage characteristics of the emitter-base junction (pn junction) change. The point is that the displacement of the probe 1a is detected.

As shown in FIGS. 6A and 6B, the bipolar transistor 102 has an element isolation region 105 in an n-type layer.
Are formed, and an emitter region 102E, a base region 102B, and a collector region 102C are formed in this portion.
03C and 103B are formed, and by using these electrodes, a change in the current-voltage characteristics of the pn junction between the emitter and the base can be amplified and taken out as an electric signal between the emitter and the collector.

In this embodiment, as in the embodiment shown in FIG.
Stress occurs at the fixed end of the emitter, and the emitter
The current-voltage characteristics of the pn junction between the bases change. Therefore, if the change in the current-voltage characteristic is detected by an external detection circuit or the like, displacement information of the probe 1a can be obtained.

Next, the cantilever chip 1 having the structure shown in FIG.
01 is described below in steps (1) to (1) shown in FIG.
This will be described with reference to (8). (1) The n-type SOI wafer 11 is used as a material.

(2) An oxide film is formed on the surface of the wafer 11,
This is patterned into a circle using photolithography technology, and silicon is etched using the oxide film 12 as a mask to form the probe 1a.

(3) Thermal oxidation is performed to form an oxide film 13 on the surface of the wafer 11. (4) An element isolation region 105 is formed by selectively implanting and diffusing boron ions in a portion (see FIG. 5) serving as a fixed end of the cantilever portion 1b.

(5) Boron ions are selectively implanted to form a p-type region (base region) 102B. (6) Phosphorus ion implantation for forming each of the emitter region 102E and the collector contact region 104C and annealing thereof are performed.

(7) Each region 102E,
After forming contact holes for 102B and 104C,
An Al film for an electrode is formed, and the Al film is patterned to form electrodes 103E, 103B, and 103C that are electrically connected to respective regions, and sintering is performed. Thereafter, the silicon on the oxide film 11a is etched into a cantilever chip shape to remove the oxide film on the cantilever portion 13.

(8) After etching the silicon from the back surface of the wafer 11 using a potassium hydroxide solution,
Is performed on the oxide film 11a by using the above. In the above steps, the chip having the structure shown in FIG. 5, that is, the bipolar transistor 102 for detecting the displacement is
Cantilever tip 10 having a structure formed at the fixed end thereof
1 is completed.

Here, in the above two embodiments, p
n-junction diode 2 or bipolar transistor 10
2 is formed only in a portion (sensor portion) for detecting the displacement of the probe. As shown in FIG. 8, a bipolar transistor 102 '(or a pn junction diode) having a similar structure is used for temperature compensation. The temperature characteristics of the element can be improved if it is formed at a position where the stress due to the bending of the cantilever portion 1b does not reach.

Also, a pn junction diode 2 for detecting displacement
The formation site of the bipolar transistor 102 is not limited to the fixed end of the cantilever portion 1b, and may be formed on the cantilever portion 1b itself.

Further, such a pn junction diode 2
Since the configuration of the bipolar transistor 102 is compatible with the integrated circuit manufacturing process, integration with other circuits is also possible. Therefore, an amplifier for output amplification can be mounted on a cantilever chip. . In this case, the SN of the displacement detection signal can be increased.

FIG. 9 is a diagram schematically showing the structure of a cantilever tip used in the embodiment of the second invention. This embodiment is characterized in that a junction field effect transistor 202 is formed at a fixed end of a cantilever portion 1b, and the displacement of a probe 1a is detected from a change in output.

The junction type field effect transistor 202
As shown in FIGS. 10A and 10B, a source region 202S, a drain region 202D and a gate region 2D are formed in an n-type layer.
In the element in which 02G is formed, electrodes 203S, 203D and 203G which are electrically connected to the respective regions are formed.

In this embodiment, when the probe 1a receives an attractive force or a repulsive force from the surface atoms of the sample and the cantilever portion 1b is bent and stress is generated at the lever fixed end portion, the cantilever portion 1b is fixed according to the stress. The output (drain current) of the junction field effect transistor 202 formed at the end changes. Therefore, if the output change is detected by an external detection circuit or the like, displacement information of the probe 1a can be obtained. Then, with the configuration shown in FIG.
If the displacement information of the probe 1a is collected while relatively moving the sample S and the probe 1a of the cantilever tip, information in the sample plane can be obtained.

Next, the cantilever chip 2 having the structure shown in FIG.
01 is described in the following steps (1) to (1) shown in FIG.
This will be described with reference to (8). (1) The n-type SOI wafer 11 is used as a material.

(2) An oxide film is formed on the surface of the wafer 11,
This is patterned into a circle using photolithography technology, and silicon is etched using the oxide film 12 as a mask to form the probe 1a.

(3) Thermal oxidation is performed to form an oxide film 13 on the surface of the wafer 11. (4) Boron ion implantation and diffusion are selectively performed on the fixed end of the cantilever portion 1b (see FIG. 9),
A source region, a drain region, and a channel region are formed.

(5) A gate region 202G is formed by selectively implanting and diffusing phosphorus ions in a portion to be a gate region. (6) After forming contact holes for each of the regions 202S and 202D and the gate region 202G in a part of the oxide film 13, an Al film for an electrode is formed by sputtering or the like, and the Al film is formed.
By patterning the film, each region 202S, 202D, 202
The electrodes 203S, 203D, and 203G that conduct to G are formed. Thereafter, sintering is performed.

(7) The silicon on the oxide film 11a is etched into a cantilever chip shape, and the cantilever portion 1 is etched.
The oxide film 13 of b is removed. (8) After etching silicon using a potassium hydroxide solution from the back surface of the wafer 11, the oxide film 11a is etched using BHF.

The chip having the structure shown in FIG.
That is, the cantilever chip 201 having the structure in which the junction field effect transistor 202 for detecting the displacement is formed at the fixed end of the cantilever portion 1b is completed.

In the above-described steps, an example in which the junction field-effect transistor is manufactured by the double diffusion method has been described. However, the present invention is not limited to this. For example, an n-type layer is epitaxially grown on a p-type wafer. Alternatively, a manufacturing method of forming an element isolation region and a gate portion in the n-type layer may be adopted. In this case, an electrochemical etching stop technique (IEEE, Transactions on Electron Devices vol.3) is used in the silicon etching performed in step (8) of FIG.
6, No. 4, 1989) to form the cantilever portion.

Here, in the embodiment shown in FIG. 9, the junction type field effect transistor 202 is formed only in the sensor portion, but as shown in FIG. Is formed at a position where stress due to bending of the cantilever portion 1b does not reach for temperature compensation, temperature characteristics of the element can be improved.

Further, the formation portion of the junction field effect transistor 202 for detecting the displacement is not limited to the fixed end of the cantilever portion 1b, but may be formed on the cantilever portion 1b itself. Further, since the structure of the junction field-effect transistor 202 is compatible with an integrated circuit manufacturing process and can be integrated with another circuit, the junction field-effect transistor can be mounted on a cantilever chip. It is also possible to mount an amplifier for output amplification, and in this case, it is possible to increase the SN of the displacement detection signal.

Here, in the scanning probe microscope of the second invention, since the junction field effect transistor is used for detecting the displacement of the probe, detection with excellent temperature stability can be performed.

That is, in the junction field effect transistor, there is a point IQ at which the operating point does not change even if the temperature changes due to the temperature characteristics of the depletion layer and the temperature characteristics of the carrier mobility (by Yamazaki and Okubo; IC and FET ”Electronics Science Series 27, refer to the industry report), so that the driving conditions (drive voltage) at which the operating point becomes IQ in the junction type field effect transistor formed on the cantilever chip are determined in advance by measurement, and the measurement results By driving the junction field effect transistor on the basis of this, a sensor having excellent temperature stability can be manufactured using the element alone.

[0048]

As described above, according to the present invention,
Displacement of a probe is detected from a change in current-voltage characteristics of a pn junction formed at least at a fixed end of a cantilever portion or a change in output of a junction field effect transistor formed at least at a fixed end of a cantilever portion. With this configuration, the cantilever chip can be provided with a self-displacement detection function, and the conventional displacement detection optical system is not required. Thereby, a scanning probe microscope having a simple configuration can be realized. Further, since the optical axis adjustment at the time of exchanging the cantilever tip is not required, the time required for observation can be reduced. Further, the scanning probe microscope can be easily applied to observation in a liquid such as a biological sample, which has attracted attention as an application of AFM observation.

[Brief description of the drawings]

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

FIGS. 2A and 2B are diagrams schematically showing the structure of a cantilever tip used in the embodiment of the first invention, wherein FIGS. 2A and 2B are a plan view and a side view, respectively.

3A and 3B are diagrams schematically showing the structure of a pn junction diode formed on the cantilever chip, wherein FIG. 3A is a detailed view of a portion A in FIG. 2 and FIG. 3B is a cross-sectional view taken along line BB of FIG.

FIG. 4 is a diagram illustrating a method for manufacturing the cantilever chip shown in FIG.

FIG. 5 is a view schematically showing another example of the structure of the cantilever tip used in the embodiment of the first invention.

6A and 6B are diagrams schematically showing the structure of a bipolar transistor formed on the cantilever chip, wherein FIG. 6A is a detailed view of a portion C in FIG. 5, and FIG. 6B is a sectional view taken along line DD of FIG.

FIG. 7 illustrates a method for manufacturing the cantilever chip shown in FIG.

FIG. 8 is a view showing a modified example of the cantilever tip used in the embodiment of the first invention.

FIG. 9 is a diagram schematically showing a structure of a cantilever tip used in the embodiment of the second invention.

10A and 10B are diagrams schematically showing a structure of a junction field-effect transistor formed on the cantilever chip, wherein FIG. 10A is a detailed view of a portion E in FIG. 9 and FIG. 10B is a sectional view taken along line FF of FIG.

FIG. 11 illustrates a method for manufacturing the cantilever chip shown in FIG.

FIG. 12 is a view showing a modified example of the cantilever tip used in the embodiment of the second invention.

[Explanation of symbols]

 1,101,201 Cantilever tip 1a Probe 1b Cantilever part 1c Pedestal 2 pn junction diode 102 Bipolar transistor 202 Junction type field effect transistor

Claims (4)

[Claims] 1. A cantilever tip having a probe, and a mechanism for relatively moving a probe of the tip and the sample in a two-dimensional direction, and detecting a displacement of the probe in the moving process to detect a surface of the sample. In the microscope for obtaining the measurement information of the microstructure of the above, a pn junction is formed on at least the fixed end of the cantilever tip on the cantilever tip, and the displacement of the probe is detected from a change in current-voltage characteristics of the pn junction. A scanning probe microscope, characterized in that the scanning probe microscope is configured to: 2. The probe according to claim 1, wherein a pn junction diode is formed at least at a fixed end of the cantilever portion, and a displacement detection signal of the probe is obtained by detecting a change in current-voltage characteristics. 2. The scanning probe microscope according to 1. 3. A bipolar transistor is formed at least at a fixed end of the cantilever, and a base thereof is formed.
2. The scanning probe microscope according to claim 1, wherein a change detection signal of the probe is obtained by amplifying and detecting a change in current-voltage characteristics of the emitter junction between the emitter and the collector. 4. A cantilever tip having a probe, and a mechanism for relatively moving the probe of the tip and the sample in a two-dimensional direction, and detecting the displacement of the probe during the moving process to detect the surface of the sample. In the microscope for obtaining measurement information of the microstructure, a junction field-effect transistor 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 output of the junction field-effect transistor. A scanning probe microscope configured to detect.