JPH08220116A - Integrated spm sensor - Google Patents

Abstract

PURPOSE: To obtain an integrated SPM sensor for detecting the torsional displacement and bending displacement at the cantilever part at quite high accuracy. CONSTITUTION: A cantilever part 25 comprises a central beam part 25a, a pair of side beam parts 25b, 25c extending along the opposite sides of the central part, and a piezoelectric resistance layer 27 formed over the entire region of the cantilever part. In order to detect a current signal flowing through the piezoelectric resistance layer independently for the central beam part and the pair of side beam parts, a first electrode 29a is connected electrically with the piezoelectric resistance layer through a contact part 31a on the fixed end side of the central beam part while second and third electrodes 29b, 29c are connected electrically with the piezoelectric resistance layer through contact parts 31b, 31c on the fixed end side of the pair of side beam parts. Furthermore, a fourth electrode 29d extending to the central beam part is connected electrically with the piezoelectric resistance layer through a contact part 31d on the free end side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated SPM sensor used in, for example, a scanning probe microscope.

[0002]

2. Description of the Related Art Conventionally, a scanning tunneling microscope (S) has been used as an apparatus for observing a conductive sample with an atomic resolution.
TM; Scanning Tunneling Microscope (Binig)
nnig) and Rohrer et al. In this STM, the samples that can be observed are limited to those that are conductive. Therefore, atomic force microscope (AFM) is used as a device that can observe an insulating sample with atomic-order resolution using STM elemental technologies such as servo technology.
rce Microsope) was proposed. This AFM is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-130302.

The AFM is equipped with a cantilever having a sharp pointed portion (probe portion) at its free end. When the probe portion is brought close to the sample, the free end of the cantilever is displaced by the interaction force (atomic force) acting between the atom at the tip of the probe portion and the atom on the sample surface. By scanning the probe along the surface of the sample while electrically or optically measuring the displacement of the free end, three-dimensional information of the sample is obtained. For example, when the probe is scanned while controlling the sample-to-sample distance so that the displacement of the free end of the cantilever is kept constant, the tip of the probe moves along the unevenness of the sample surface.
A three-dimensional image showing the surface shape of the sample can be obtained from the position information of the tip of the probe.

In the AFM, a displacement measuring sensor for measuring the displacement of the cantilever is generally provided separately from the cantilever. However, recently, an integrated SPM sensor in which the cantilever itself has a function of measuring displacement has been proposed by "M. Tortonese" et al.
This integrated SPM sensor is, for example, "M. Toronese, HY
anada, RCBarrett and CFQuate, Transducers and
Sensors'91: Atomic force microscopy using a piezore
sistive cantilever ”and PCT application WO92 / 1239
8 are disclosed.

Since such an integrated SPM sensor is extremely simple and compact in size, it is expected that a so-called stand-alone AFM that moves the cantilever side can be configured. In the conventional AFM, since the sample is moved in the XY directions to change the relative positional relationship between the tip of the cantilever and the probe, the size of the sample is limited to about several cm at the maximum.
There is an advantage that the limitation of the size of the sample can be removed.

A method of manufacturing the above-described integrated SPM sensor will be described below with reference to FIG. As shown in FIG. 4A, for example, a bonded silicon wafer 1 in which a silicon layer 7 is provided on a silicon wafer 3 via a silicon oxide separation layer 5 is prepared. Next, boron (B) is implanted into the very surface of the silicon layer 7 by ion implantation to form the piezoresistive layer 9, and
After patterning into the shape shown in FIG. 3D, the surface is covered with the silicon oxide film 11. Then, a hole for bonding is made on the fixed end side of the cantilever, and aluminum is sputtered to form the electrode 13.

Further, a resist layer 15 is formed on the lower side of the silicon wafer 3, and the resist layer 15 is patterned to form openings as shown in FIG. 4 (b). Then, after heat treatment for making ohmic contact, the silicon wafer 3 is etched to the separation layer 5 by wet anisotropic etching using the patterned resist layer 15 as a mask, and finally, the lower portion of the cantilever portion 17 is etched with hydrofluoric acid. By etching the separation layer 5 of FIG. 4, the integrated SPM sensor having the first and second beam portions 17a and 17b connected at the free end side thereof is completed as shown in FIGS. 4 (c) and 4 (d). To do. Note that FIG. 4 (d)
Shows a top view of such an integrated SPM sensor.

In the integrated SPM sensor thus manufactured, the first and second beam parts 17 are used for the measurement.
A DC voltage of several volts or less is applied between the two electrodes 13 provided on the fixed end side of the a and 17b, and the cantilever portion 1
The free end of 7 is brought close to the sample (not shown). When an atomic force acts between the free end of the cantilever portion 17 and the atoms on the sample surface (not shown), the cantilever portion 17 is displaced. The resistance value of the piezoresistive layer 9 changes accordingly, so that the displacement of the cantilever portion 17 is changed to the two-electrode 1
It is obtained as a current signal flowing during 3.

[0009]

By the way, generally, the displacement of the cantilever portion 17 includes a displacement due to "twisting" and a displacement due to a normal "warp". However, in the conventional integrated SPM sensor, the displacement of the cantilever portion 17 is simply regarded as the change in the current signal flowing between the two electrodes 13, and therefore the change in the current signal is caused by the “torsion displacement”. It was not possible to determine whether it was caused by "warp displacement". Specifically, in the conventional integrated SPM sensor, the change of the current signal flowing between the two electrodes 13 is simply changed.
The warp displacement of 7 is detected. Therefore, even when the torsional displacement and the warp displacement occur at the same time, the change in the detected current signal is regarded as the warp displacement.
As a result, there is a problem that it is not possible to perform highly accurate measurement on the sample surface.

[0010]

Therefore, for the purpose of catching the torsional displacement as a change of the current signal (that is, a change of the LFM signal), as shown in FIG. 2C, the first and second beams are Consider an integrated SPM sensor with a third beam section 17c between sections 17a, 17b. In addition, reference numerals R ₁ and R ₃ in the figure indicate resistance values of the piezoresistive layer 9 (see FIG. 4) of the first and second beam portions 17a and 17b, and reference numeral R ₂ indicates a third beam portion. 17c shows the resistance value of the piezoresistive layer 9, and the power source 19 is connected to the first and second beam portions 17a and 17b via the electrode 13. The free end side of the third beam portion 17c is electrically connected to the first and second free ends,
The fixed end side is grounded. In addition, from the power source 19 via the first and second beam units 17a and 17b,
Current signals (I ₁ , I ₂ ) flowing in the third beam 17c
Is configured to be detected by an ammeter 21 arranged in the electric paths of the first and second beam portions 17a and 17b.

In such a structure, it is now assumed that the cantilever portion 17 is displaced and warpage displacement and twist displacement are generated. When the cantilever portion 17 is displaced, the resistance value of the piezoresistive layer 9 (see FIG. 4) changes, so that the current signals (I ₁ , I ₂ ) flowing through the piezoresistive layer 9 change. At this time, the displacement is electrically detected by detecting a change in the current signals (I ₁ , I ₂ ) by the ammeter 21.

Specifically, torsional displacement (LFM signal)
Is defined by the difference “I ₁ −I ₂ ” of the current signals, and the warp displacement (AFM signal) is the sum of the current signals “I ₁ +
I ₂ ″.

Here, when the cantilever portion 17 is displaced, the first and second beam portions 17 are supplied from the power source 19.
Among the current signals flowing in the third beam 17c via a and 17b, the current signals resulting from the twist displacement are respectively I
_1N , I _2N , and the current signals caused by the warp displacement are I _1S , I
_2S, and the current signals due to other factors are I ₁₀ and I ₂₀ , respectively, the current signals (I ₁ , I ₂ ) flowing in the electric path due to the displacement of the cantilever portion 17 are I _It is expressed as ₁ = I ₁₀ + I _1N + I _1S I ₂ = I ₂₀ + I _2N + I _2S .

Now, in the initial state in which the twist displacement and the warp displacement do not occur, the current signals (I ₁₀ , I ₂₀ ) are considered to be at the same level as each other, so that I ₁₀ = I ₂₀ = I ₀ can be expressed. . Further, when only the warp displacement is generated, the warps of the first and second beam portions 17a and 17b are equal to each other, and thus I _1S = I _2S = I _S can be expressed.

Under these conditions, when the difference "I ₁ -I ₂ " between the current signals corresponding to the torsional displacement and the sum "I ₁ + I ₂ " of the current signals corresponding to the warp displacement are calculated, the torsional displacement is calculated. _{= I 1 -I 2 = I 0} + I 1N + I S - (I 0 + I 2N + I S) = I 1N -I 2N warp displacement _{= I 1 + I 2 = I} 0 + I 1N + I S + (I 0 + I 2N + I S ) = 2I ₀ + 2I _S + I _1N + I _2N .

As a result, it becomes possible to detect the torsional displacement, which could not be detected by the conventional method, and it is possible to measure the surface information of the sample with high accuracy. However, since the current signal (I _1N + I _2N ) corresponding to the twist is mixed in the current signal corresponding to the warp displacement, a sufficiently satisfactory measurement result can be obtained when the sample is scanned with extremely high accuracy. Is difficult. Therefore, there is a demand for the development of a scanning SPM sensor that can perform extremely highly accurate sample scanning.

The present invention has been made to meet such a demand, and an object thereof is to provide an integrated SPM sensor capable of detecting the torsional displacement and the warp displacement of the cantilever portion with extremely high accuracy. To provide.

In order to achieve such an object, the present invention has a free end and a fixed end, and the free end is displaceable by supporting the fixed end. An integrated SPM sensor having a central beam portion, the central beam portion extending from the fixed end toward the free end, and the central beam portion being disposed on both sides of the central beam portion. And a pair of side beam portions extending along the free end and interconnected with the central beam portion, and a conductive piezoresistive layer formed over the entire area of the cantilever portion. , So that the current signal flowing through the piezoresistive layer is independently detected for each of the central beam part and the pair of side beam parts. A first electrode electrically connected to the anti-layer, second and third electrodes electrically connected to the piezoresistive layer at fixed ends of the pair of side beam portions, and a predetermined portion of the cantilever portion. And a fourth electrode electrically connected to the piezoresistive layer at the site.

[0019]

According to the present invention, the current signal flowing in the central beam portion is detected by detecting the current signal flowing from the first electrode to the fourth electrode, and at the same time, the second and third electrodes are detected. To the fourth electrode, the current signals flowing through the pair of side beam portions are independently detected.

[0020]

EXAMPLE An integrated SPM according to an example of the present invention will be described below.
The sensor will be described with reference to FIGS. 1 to 3. As shown in FIGS. 1A and 2A, the integrated SPM sensor of this embodiment has a free end and a fixed end supported by a supporting member 23, and this fixed end supports the fixed end. Accordingly, the cantilever portion 25 having a free end that can be displaced is provided.

The cantilever portion 25 has a central beam portion 25a extending from the fixed end toward the free end, and central beam portions 25a arranged on both sides of the central beam portion 25a.
A pair of side beam portions 25b, 25c which extend along and are interconnected with the central beam portion 25a at their free ends.
And a conductive piezoresistive layer 27 formed over the entire area of the cantilever portion 25.

Further, the current signal flowing through the piezoresistive layer 27 is transmitted by the central beam portion 25a and the pair of side beam portions 25.
The contact portion 31 formed on the fixed end side of the central beam portion 25a so as to be independently detected for each of b and 25c.
The first electrode 29a electrically connected to the piezoresistive layer 27 via a and the piezoresistive layer 27 via the contact portions 31b and 31c formed on the fixed ends of the pair of side beam portions 25b and 25c, respectively. There are provided second and third electrodes 29b and 29c electrically connected to each other, and a fourth electrode 29d electrically connected to the piezoresistive layer 27 at a predetermined portion of the cantilever portion 25.

In the case of the present embodiment, the fourth electrode 29d is arranged on the central beam portion 25a so as to extend along the central beam portion 25a, and the contact portion 31d (formed on the free end side thereof). It is electrically connected to the piezoresistive layer 27 through (see FIG. 2A).

FIG. 2A is a sectional view taken along the line II-II of FIG. 1A and shows a vertical sectional view of the central beam portion 25a of the cantilever portion 25. As shown in FIG. 2A, the cantilever portion 25 applied to this embodiment is
The lever structure portion 33 made of a silicon layer, the piezoresistive layer 27 formed on the lever structure portion 33, and the insulating layer 35 formed on the piezoresistive layer 27 are provided. The piezoresistive layer 27 is formed by ion-implanting boron (B) on the surface of the lever structure portion 33 made of a silicon layer, and at the same time, the probe 37 is formed at the free end. .

Further, the first to fourth electrodes 29a, 29b, 29c, 29 shown in FIGS. 1 (a) and 2 (a) are used.
d is electrically connected to the piezoresistive layer 27 via contact portions 31a, 31b, 31c, 31d formed by cutting the insulating layer 35, respectively. Therefore, the insulating layer 35
Is the piezoresistive layer 27 excluding the contact portions 31a, 31b, 31c of the first to third electrodes 29a, 29b, 29c and the contact portion 31d of the fourth electrode 29d (that is, around the probe 37). Is covered on the side surface of the lever structure portion 33.

The fourth electrode 29d is formed so as to extend from the fixed end side to the free end side so as to cover a part of the insulating layer 35 of the central beam portion 25a, and at the free end side thereof, The probe 37 is covered.

The fixed end of such a cantilever portion 25 is supported by a supporting member 23, and the supporting member 23 has insulating layers 39, 4 which are silicon oxide layers on both sides.
1 is formed by the silicon substrate 43.

Next, the operation of the integrated SPM sensor of this embodiment will be described. In the integrated SPM sensor of this embodiment, the current signal flowing through the piezoresistive layer is the central beam portion 2.
5a and the pair of side beam portions 25b and 25c, the first to third electrodes 29 so that they can be detected independently.
The a, 29b, and 29c are connected to the power supply 47 through the first to third ammeters 45a, 45b, and 45c, respectively, and the fourth electrode 29d is grounded.

Therefore, by the power source 47, the fourth electrode 29d and the first electrode 29a, the fourth electrode 29d and the second electrode 29b, and the fourth electrode 29d and the third electrode 29c are connected. A predetermined voltage is applied to each.

At this time, the piezoresistive layer 27 is supplied from the power source 47 through the first to third electrodes 29a, 29b, 29c.
The current signal flowing through the first to third ammeters 45a,
The central beam portion 25a and the pair of side beam portions 25b and 25c are independently detected by 45b and 45c.

When the cantilever portion 25 is displaced when measuring the surface information of the sample (not shown), the displacement includes a warp displacement and a torsional displacement. When the cantilever portion 25 is displaced in this manner, the piezoresistive layer 27
Of the piezoresistive layer 27, the current signal flowing through the piezoresistive layer 27 changes. At this time, the displacement (that is, the warp displacement and the twist displacement) of the cantilever portion 25 can be electrically detected by detecting the change of the current signal by the first to third ammeters 45a, 45b, 45c. .

FIG. 1B shows a circuit configuration of the integrated SPM sensor shown in FIG. 1A. Reference numerals R ₁ and R _{3 in} the figure denote a pair of side beam parts. 25b,
The resistance value of the piezoresistive layer 27 of 25c is indicated by a symbol R ₂
Indicates the resistance value of the piezoresistive layer 27 of the central beam portion 25a. Then, in the same drawing, corresponding to the displacement of the cantilever portion 25, the piezoresistive layer 27 of the central beam portion 25a and the pair of side beam portions 25b and 25c are respectively
It is assumed that the current signals I ₂ and I ₁ , I ₃ are flowing.

Under such conditions, the integrated type S of this embodiment is
In the PM sensor, the twist displacement (LFM signal) is
It is defined by the difference "I ₁ -I ₃ " between the current signals, and
The warp displacement (AFM signal) is defined by the value "I ₂ " of the current signal.

Here, when the cantilever portion 25 is displaced, the current signal I ₂ flowing through the central beam portion 25a.
Among them, the current signal caused by the twist displacement is I _2N , the current signal caused by the warp displacement is I _2S, and the current signal caused by other factors is I ₂₀ . On the other hand, the current signals (I ₁ , I 2) flowing through the pair of side beam portions 25a, 25b
_{In 3} ), the current signals due to the twist displacement are I _1N and I _3N , respectively, and the current signals due to the warp displacement are I _1S and I _1S , respectively.
I _3S and current signals caused by other factors are I ₁₀ and I ₃₀ , respectively.

At this time, the current signal I ₂ flowing through the central beam portion 25a and the pair of side beam portions 25b, 25
The current signals I ₁ and I ₃ flowing through c are expressed as I ₁ = I ₁₀ + I _1N + I _1S I ₂ = I ₂₀ + I _2N + I _2S I ₃ = I ₃₀ + I _3N + I _3S .

Now, in the initial state in which the twist displacement and the warp displacement do not occur, the current signals (I ₁₀ , I ₂₀ , I ₃₀ ) are considered to be at the same level with each other, so I ₁₀ = I ₂₀ = I ₃₀ = I
It can be represented as ₀ . In the case where only warp displacement occurs, the central beam part 25a and a pair of side beam part 25b, 25c warpage amount of for are equal to each other, and _{I 1S = I 2S = I 3S} = I S Can be represented.

Under these conditions, the difference "I ₁ -I ₃ " between the current signals corresponding to the torsional displacement is calculated. Torsional displacement = I ₁ -I ₃ = I ₀ + I _1N + I _S- (I ₀ + a _{I 3N + I S) = I} 1N -I 3N.

Further, since the central beam portion 25a is in a state where the torsional displacement is unlikely to occur, the current signal I _2N due to the torsional displacement has an extremely small value (I _S >> I _2N ). As a result, the value of the current signal I _2N can be neglected in the calculation. As a result, under the above conditions, the value "I ₂ " of the current signal corresponding to the warpage displacement is warpage displacement = I ₂ = I ₀ + I _S.

As a result, it has been found that the twist displacement (LFM signal) and the warp displacement (AFM signal) of the cantilever portion 25 can be detected with extremely high accuracy. As described above, the integrated SPM sensor of this embodiment has the central beam portion 25a.
And the current signals flowing through the piezoresistive layers 27 of the pair of side beam portions 25b and 25c can be independently detected. Therefore, the displacement of the central beam portion 25a and the pair of side beam portions 25b and 25c can be detected. It becomes possible to detect independently. As a result, the cantilever part 2
The torsional displacement (LFM signal) and the warp displacement (AFM signal) of No. 5 can be detected with extremely high accuracy.

Further, the fourth electrode 2 applied to this embodiment
Since 9d is grounded, the potential near the probe 37 can be maintained at the ground potential (that is, 0 [V]). As a result, the electrostatic force acting between the sample surface and the probe 37 can be removed, so that the measurement accuracy can be maintained at a constant level.

As the power supply 47 applied to this embodiment, either a DC voltage power supply or an AC voltage power supply may be used. Further, although the fourth electrode 29d is arranged on the surface of the central beam portion 25a on the probe 37 side in the above-described embodiment, for example, the back surface of the central beam portion 25a (that is, the probe 37 is provided). It may be arranged on the surface opposite to the surface on which it is formed. Furthermore, the fourth electrode 29d can be arranged on either surface of the pair of side beams 25b and 25c.

Further, the central beam portion 25a suppresses the torsional displacement of the cantilever portion 25 within an allowable range,
It is also preferable that the width is made larger than the width of the pair of side beam portions 25b and 25c.

Next, a method of manufacturing the integrated SPM sensor of the present embodiment having the above-mentioned effects will be briefly described with reference to FIG. In the following description, the probe 3
The process of manufacturing 7 is omitted.

As shown in FIG. 3, for example, a bonded silicon wafer in which a silicon layer 33 is provided on a silicon substrate 43 with a silicon oxide separation layer 39 interposed therebetween is prepared. Next, an oxide film 41 is formed on the lower surface of the silicon substrate 43, and an oxide film 49 is formed on the upper surface of the silicon layer 33. Then, boron (B) is implanted into the extreme surface of the silicon layer 33 by ion implantation to piezo-process. Resistance layer 2
7 is formed (see FIG. 7A).

After the silicon layer 33 and the piezoresistive layer 27 are patterned into the shape shown in FIG. 3B, the entire surface is covered with a silicon oxide film 35 which functions as an insulating layer (see FIG. 2B).

Next, a hole for bonding is made in the portion corresponding to the fixed end side and the free end side of the cantilever portion 25, and then metal is sputtered in this hole portion to form the first to fourth electrodes 29a. , 29b, 29c, 29d are formed (see FIG. 1C and FIG. 1A).

Subsequently, in order to make ohmic contact, a heat treatment is applied to the silicon wafer having the shape shown in FIG. 9B, and then the first to fourth electrodes 29 are formed.
In order to protect a, 29b, 29c and 29d, the surfaces of these electrodes are covered with polyimide 51. Then, using the oxide film 41 as a mask, the silicon substrate 43 is etched up to the separation layer 39 by wet anisotropic etching (see FIG. 3D).

Finally, the separation layer 39 below the cantilever portion 25 is etched with hydrofluoric acid to complete an integrated SPM sensor having a central beam portion 25a and a pair of side beam portions 25b and 25c (see FIG. ) And FIG. 1 (a)).

[0049]

The integrated SPM sensor of the present invention is configured so that the current signals flowing through the piezoresistive layers of the central beam portion and the pair of side beam portions can be independently detected. The displacements of the pair of side beam portions can be detected independently. As a result, the torsional displacement (LFM signal) and the warp displacement (AFM signal) of the cantilever portion can be detected with extremely high accuracy.

[Brief description of drawings]

FIG. 1A is an integrated SP according to an embodiment of the present invention.
The top view which shows the structure of M sensor schematically, (b) is a figure which shows the circuit structure of the integrated type SPM sensor which concerns on one Example of this invention roughly.

2A is a cross-sectional view taken along line II-II shown in FIG. 1A, and FIG. 2B is a side surface of the cantilever portion on the free end side as viewed from the direction of arrow b in FIG. 2A. FIG. 1C is a diagram schematically showing the circuit configuration of the basic principle of the integrated SPM sensor according to the embodiment of the present invention.

3A to 3E are views showing a manufacturing process of an integrated SPM sensor according to an embodiment of the present invention, respectively.

4A to 4D are respectively conventional integrated SPMs.
The figure which shows the manufacturing process of a sensor.

[Explanation of symbols]

25 ... Cantilever part, 25a ... Central beam part, 25
b, 25c ... Side beam part, 27 ... Piezoresistive layer, 2
9a ... 1st electrode, 29b ... 2nd electrode, 29c ... 3rd
Electrode, 29d ... Fourth electrode, 31a, 31b, 31c
… Contact section.

Claims (3)

[Claims] 1. An integrated SPM sensor having a cantilever portion having a free end and a fixed end, and the free end being displaceable by supporting the fixed end, The cantilever portion has a central beam portion extending from the fixed end toward the free end, and a central beam portion disposed on both sides of the central beam portion and extending along the central beam portion. A pair of side beam portions interconnected with a beam portion and a conductive piezoresistive layer formed over the entire area of the cantilever portion are provided, and a current signal flowing through the piezoresistive layer is at the center. A first electrode electrically connected to the piezoresistive layer on the fixed end side of the central beam part so that the beam part and the pair of side beam parts are detected independently of each other;
Second and third electrodes electrically connected to the piezoresistive layer on the fixed end sides of the pair of side beam portions, respectively, and a fourth electrode electrically connected to the piezoresistive layer at a predetermined portion of the cantilever portion. An integrated SPM sensor, characterized in that the electrodes are provided. 2. The fourth electrode is arranged on the central beam portion so as to extend along the central beam portion, and is electrically connected to the piezoresistive layer on the free end side. The integrated SPM according to claim 1, wherein
sensor. 3. A width of the central beam portion is larger than a width of the pair of side beam portions so as to suppress twist displacement of the cantilever portion within an allowable range. Item 1. The integrated SPM according to item 1 or 2.
sensor.