CN1303414C

CN1303414C - Dielectric loss microscope with scanning probe and measuring method therefor

Info

Publication number: CN1303414C
Application number: CNB2004100776165A
Authority: CN
Inventors: 丁喜冬; 熊小敏; 张进修
Original assignee: National Sun Yat Sen University
Current assignee: Sun Yat Sen University; National Sun Yat Sen University
Priority date: 2004-12-28
Filing date: 2004-12-28
Publication date: 2007-03-07
Anticipated expiration: 2024-12-28
Also published as: CN1632516A

Abstract

The present invention relates to a scanning probe microscope for dielectric loss and a measurement method thereof. The microscope comprises a PZT scanning tube, a conductive metal probe, a non-conductive sample whose lower surface is provided with a conductive layer, a scanning tunnel microscope controller, a frequency signal generation and phase detector, a front amplifier and a microcomputer. The present invention adopts an AC bias method with little DC components or without DC components. Frequencies near the peak value of a curve describing the change of capacitance between the probe and a sample to be measured and a dielectric loss angle with frequencies or a plurality of frequencies at the biggest slope change point are selected as work frequency. The capacitance (voltage characteristics) and a lag phase angle of alternating current lagging behind alternating voltage are used as the feedback quantity and the display quantity of a two-directional image. The apparent capacitance two-directional image and the apparent dielectric loss two-directional image of an object to be measured can be simultaneously obtained during the two-dimensional scanning of the probe at a time. The true dielectric loss two-directional image of a test sample can be obtained by carrying out subtraction for the two images. Dielectric structures which can not be displayed by other methods, particularly interface details, can be displayed in the dielectric loss two-directional image.

Description

Dielectric loss scanning probe microscopy and measuring method thereof

Technical field

The present invention relates to a kind of surveying instrument, particularly a kind of dielectric loss probe scanning microscope and measuring method thereof.

Background technology

Existing scanning tunnel microscope (STM) all is to work under Dc bias usually, but its modified has various working method, and scanning capacitance microscope (SCM) has wherein used under AC bias works.In the measurement of contact SCM, can provide the two dimensional image of carrier moving in the semiconductor samples by the variation of leakage current; The contact scanning capacitance microscope of making on atomic force microscope (AFM) basis (LM-SCM) then is a two dimensional image of measuring the conducting sample surface capacitance.The microscopical report of above-mentioned scanning capacitance, used apparatus and method and measuring object are all different with the present invention, existing scanning capacitance microscope is not determined frequency of operation and is carried out two-dimensional scan with this frequency with the variation of frequency by the drag angle of current amplitude and electric current, thereby can not obtain the electric capacity two-dimensional image of measured surface and the two-dimensional image of dielectric loss simultaneously.

Summary of the invention

The purpose of this invention is to provide a kind of dielectric loss probe scanning microscope and measuring method thereof, sample is non-conductive (dielectric) material, apparatus of the present invention and measuring method can study and measure non-conductive sample measured surface more Donna meter ruler cun the dielectric structure details and its two-dimentional microcell scan image is provided.

Dielectric loss scanning probe microscopy of the present invention includes non-conductive sample and the microcomputer system that PZT scanatron, conducting metal probe, scanning tunnel microscope STM controller, prime amplifier, frequency generation and phase detectors, lower surface have conductive layer, the frequency of signal generator and the phase detectors that it is characterized in that on conducting metal probe or sample connecting scalable DC component bias voltage and exchange carrier wave, frequency signal take place and phase detectors also while and scanning tunnel microscope controller be connected with microcomputer system (Fig. 1).

Important feature of the present invention is: the direct current measurement that will have now in the probe tunnel flying-spot microscope makes AC measurment into, and sample is non-conductive (dielectric) material that lower surface has a conductive layer; AC response amplitude A (being proportional to electric capacity) and dielectric loss angle δ by sample select the frequency of operation (see figure 3) with peak value on the change curve of frequency or curve steepest place.When conducting probe and sample near the time, to there be certain electric capacity between the conductive layer of conducting probe and sample lower surface, when applying alternating signal, because the polarization induced electricity in the sample lags behind the voltage signal that applies, the exchange current (Fig. 2) and the corresponding energy loss angle of voltage signal will appear lagging behind on the phase angle in sample.From equivalent electrical circuit, can be the in parallel of electric capacity and a resistance with circuit equivalent between the sample lower surface conductive layer with conducting probe.At this moment, if between conducting probe and sample lower surface conductive layer, apply an ac voltage signal V, just can on probe, detect the alternating current I that produces because of sample (dielectric) polarization.Utilize PZT piezoelectric scanning pipe that probe (its height is represented with Z) is also measured capacitance C simultaneously near non-conductive sample upper surface, until the variable quantity of C value with after the variable quantity of Z becomes reciprocal relation, at this moment, the distance of probe and sample is in the same order of magnitude with the radius-of-curvature of probe tip, keeps Z constant then.After this concrete measuring method can be by carrying out one of in the following manner:

1, permanent high mode: cut off STM in the feedback of Z direction to keep the height constant (but the distance of probe and sample surfaces then changes with the fluctuating of sample surfaces) of probe, probe is scanned on sample and measure capacitance C simultaneously and polarization lags behind the drag angle δ of voltage signal, can obtain the X-Y scheme of electric capacity and dielectric loss from C value and δ value with the variation that scans.

2, permanent capacitive way: the amplitude signal (being proportional to electric capacity) with electric current is a feedback quantity, probe is scanned on sample and measures loss angle, obtains the X-Y scheme of loss; Simultaneously, the control signal of the last Z direction of extraction PZT can obtain the shape appearance figure of permanent electric capacity.

3, permanent loss mode: the lagging phase angle signal (being approximately loss) with electric current is a feedback quantity, and probe is scanned on sample, obtains the X-Y scheme of electric capacity; Simultaneously, the control signal of the last Z direction of extraction PZT can obtain the shape appearance figure of permanent loss.

PZT piezoelectric scanning pipe drives probe and moves on sample surfaces by one of above-mentioned three kinds of working methods in X, Y, three sides of Z under the control of computing machine and feedback circuit, distance and the position of probe on sample between control probe and the sample, thereby probe is scanned at sample surfaces, obtain the electric capacity of sample and the X-Y scheme of dielectric loss angle.

During measurement, after distance between probe and sample is determined, earlier record the AC response amplitude A (being proportional to electric capacity) of sample and dielectric loss angle δ change curve (see figure 3) with frequency with the method for quasi-continuous frequency conversion, carry out two-dimensional scan with one or several frequencies at crest frequency on this change curve or slope variation steepest place then, then can obtain the electric capacity two-dimensional image of one or several measured surfaces and the two-dimensional image of one or several dielectric loss angles simultaneously.

Concrete measuring process is:

1) earlier fixed point obtains characterizing the voltage of capacitance size and the electric polarization course lagging phase angle δ change curve with frequency, i.e. A-f and δ-f curve with frequency sweeping.

Frequency of operation when 2) several frequencies near frequency selection δ-f curve or the A-f curve upward peak or rate of curve steepest place are as two-dimensional scan.

3) the alternation carrier wave being arranged and have (or not having) Dc bias and becoming under the condition of work of image current, make feedback quantity and demonstration amount, measured permanent high mode apparent capacity figure, apparent dielectric loss figure and real dielectric loss figure with electric capacity or loss angle δ; The X-Y scheme of the electric capacity that loss X-Y scheme during the perseverance capacitive way and permanent electric capacity shape appearance figure and permanent loss angle mode record and the shape appearance figure of permanent loss.

The present invention can record the various microcell images of scan area from 30 μ m * 30 μ m to 2nm * 2nm according to Testing requirement.

The drawing explanation

Below in conjunction with accompanying drawing the present invention is described in further detail.

Fig. 1 is the structure principle chart of dielectric loss probe scanning microscope SDDM.

Fig. 2 is that alternating current lags behind the synoptic diagram of the lagging phase angle of alternating voltage with frequency change.

The I-f and the δ-f curve of the arbitrfary point that Fig. 3 obtains when being spot frequency scanning.

Fig. 4 is the two dimensional image that obtains in single pass of dielectric loss probe scanning microscope (2000nm * 2000nm).Wherein (A) is SDDM apparent capacity two dimensional image, (B) is the apparent loss angle X-Y scheme of SDDM, is SDDM dielectric loss angle X-Y scheme (C), obtained by the B-A computing).

Among Fig. 1, microscope by PZT scanatron 5, conducting metal probe 6, lower surface have conductive layer non-conductive (dielectric) sample 7, have feedback circuit 21, high pressure amplify 22 and bias voltage scanning tunnel microscope controller 2, the prime amplifier 4 of 23 performances, the phase-detection device 3 that has frequency of signal generator 31 and the microcomputer system (band Control Software and display) 1 that superpose form.Between conducting metal probe 6 and sample 7 by 23 with scalable DC component bias voltage and the signal that exchanges carrier amplitude on 31 are connected.Measurement mechanism of the present invention can also add a sample resistance or prime amplifier between probe and lock-in amplifier.

Among Fig. 2, ordinate is the relative value of electric current and voltage, and abscissa is phase angle ω t.The position preceding curve be ac voltage signal, after be AC current waveform, the phase angle that electric current lags behind voltage is designated φ in the drawings.

Among Fig. 3, left ordinate be electric capacity (characterize with voltage: the μ V of unit); Right ordinate is phase angle δ (degree of unit, a degree), and abscissa is a frequency, and unit is KHz.δ-f peak of curve is in about 20KHz place.Therefore frequency of operation can scan out corresponding two dimensional image near being selected in 20KHz.

Embodiment

Measure embodiment:

Sample: the bismuth titanate film surface of magnetron sputtering

Step:

1, earlier after the fixed point spacing, obtain AC response amplitude A and dielectric loss lagging phase angle δ change curve, i.e. A-f and δ-f curve with frequency with frequency sweeping.Fig. 3 has provided the A-f and the δ-f curve of actual measurement.

2, the frequency of operation in the time of can selecting δ-f peak of curve place or slope steepest place as two-dimensional scan.This measures the 20KHz that selects near δ-f peak of curve place is frequency of operation.Certainly, also can select several other frequencies to scan simultaneously as frequency of operation.So just can obtain more information.

3, measurement parameter: survey frequency is 20kHz, and alternating voltage is 8mV, and dc partial voltage is zero; Resolution is 256 * 256.The image that is obtained is seen Fig. 4.Wherein (A) is apparent SDDM electric capacity X-Y scheme; (B) be apparent SDDM dielectric loss X-Y scheme; (C) be SDDM dielectric loss X-Y scheme.In figure (A), both included the information of electric capacity, also included the information of probe and sample distance, so be called the apparent capacity X-Y scheme; In figure B, both included the information of dielectric loss, also included the information of probe and sample distance, so be called apparent dielectric loss X-Y scheme; Adopt the compute mode of A-B, eliminate the information of probe and sample distance basically after, can obtain the SDDM dielectric loss X-Y scheme shown in the figure (C).By figure (C) as seen, it is clearly shown that the details of the interface portion that can not obtain with additive method.

Claims

1, a kind of dielectric loss scanning probe microscopy, include non-conductive sample and microcomputer system that PZT scanatron, conducting metal probe, scanning tunnel microscope STM controller, prime amplifier, frequency signal generation and phase detectors, lower surface have conductive layer, it is characterized in that the frequency signal that connects scalable DC component bias voltage and exchange carrier wave on conducting metal probe or sample takes place and phase detectors, frequency signal takes place also to be connected with microcomputer system with the scanning tunnel microscope controller simultaneously with phase detectors.

2, a kind of measuring method of using the dielectric loss scanning probe microscopy is characterized in that the measuring process of this method is:

1) earlier fixed point obtains characterizing the voltage of capacitance size and the electric polarization course lagging phase angle δ change curve with frequency, i.e. A-f and δ-f curve with frequency sweeping;

Frequency of operation when 2) several frequencies near frequency selection δ-f curve or the A-f curve upward peak or rate of curve steepest place are as two-dimensional scan;

3) the alternation carrier wave is being arranged and be with or without Dc bias and become under the condition of work of image current, the apparent capacity X-Y scheme when recording permanent high mode, apparent dielectric loss X-Y scheme and real dielectric loss X-Y scheme; When the loss X-Y scheme during permanent capacitive way and permanent electric capacity shape appearance figure and permanent loss mode electric capacity X-Y scheme and permanent loss shape appearance figure.