JP2848539B2 - Cantilever deflection sensor and method of using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to, for example, an atomic force microscope (AFM).
To measure the force or deflection of a cantilever-type element used in the field of: The invention further relates to a method and an apparatus for determining material properties. In particular, it relates to a scanning probe microscope based dopant profiler with the generation and detection of harmonics of the applied electromagnetic field.

BACKGROUND OF THE INVENTION It was first known in U.S. Pat. No. 4,727,318 and is described by G. Binning, CF Quate and Ch. Gerber in Phys. Rev. Letters, Vol. 56, No. 9, 198.
The atomic force microscope described in March, 6 pp. 930-933,
Use a sharp pointed tip mounted on a spring-like cantilever beam to scan the profile of the surface to be investigated. At the required distance, a small force is created between the atom at the tip of the tip and the atom at the surface, resulting in a slight swing of the cantilever. In U.S. Patent No. A4724138, a conductive tunnel tip is placed within a tunnel distance behind a cantilever beam, which is also conductive, and this deflection is measured by a tunnel microscope to determine the deflection using changes in tunnel current. . With the properties of the cantilever beam known, the force generated between the AFM tip and the surface under investigation can be determined.

The force that develops between the sharp tip and the surface is typically van der Waalska, covalent, ionic, or core repulsion.

An important aspect of AFM is to accurately determine cantilever deflection. One group of such shake measurement methods is based on coupling the cantilever to another distance sensitive microscope. Combinations of cantilevers and scanning tunneling microscopes are described, for example, in the aforementioned U.S. Pat. No. 4,747,318. Another approach using microwave coupled sensors is scanning near-field optical microscopy (SNOM)
Also known as scanning tunneling optical microscope (STOM), Ultramicroscopy 42-44 (1992), pp. 1668-16, by Diaspro and Aguilar.
70.

Another group of detection methods is based on the well-known piezoelectric or piezoresistive effect. An example is Appl. Phys Lett. 62 by M. Tortonese et al.
(8), 1993, pp. 834-836. These methods provide a detection scheme that incorporates a shake detector into the cantilever.

Yet another possible method of detecting cantilever displacement is based on the detection of capacitance, see Joyce et al., Rev. Sci. Instr. 62 (1991), p. 710,
J. Vac.S by Gddenhenrich et al.
ci.Technol.A8 (1990), p.383, and European Patent Application A029
Known from 0648.

In the method known from the above-mentioned application and U.S. Pat. No. 4,485,671, the bending of a flexible element is measured by using the change of the resonance frequency and its harmonics. The frequency is detected by a crystal oscillator or a capacitance additionally mounted on the cantilever.

The displacement of the flexible element can be measured using an optical method such as a beam deflection method or an interferometer. In the beam deflection method, the length of the lever is used. Generally,
The lever is irradiated with a light beam, preferably generated by a laser diode or guided through an optical fiber. A small deflection of the lever causes a moderate change in the angle of reflection, which causes a deflection of the reflected light beam, which is measured by a bicell or other suitable photodetector. The beam deflection method is simple and reliable. This is because, for example, by Myer and Amer, Appl.Phys.Let
t.53 (1988), pp. 1045-1047. Interferometer usage is described, for example, by Martin et al.
Appl. Phys. 61 (1987), p. 4723, Opt. Lett. 12 (1288) by Salid et al., P. 1057, and Oshio (Osh).
io) Ultramicroscopy 42-44 (1992), pp. 310 by others.
314. SP by creating a cantilever with extremely high resonance frequency while maintaining Q
Since the sensitivity of M can be increased, the cantilever tends to be smaller. With such cantilevers, the aforementioned optical methods are liable to fail due to reduced reflectivity and problems arising from the limitation of the focal size of the laser beam.

Today's very large scale integrated circuit (VLSI) technology requires accurate knowledge of the spatial extent, density, or dispersion in all three dimensions of the active component (dopant) introduced into a substrate or main material. The most common devices made with VLSI are bipolar or metal oxide semiconductor field effect transistors (MOSFETs), diodes, and capacitors. Its characteristic length scale is currently about 0.
5 microns, but in the future 350nm or even 100n
will be reduced to m. Arsenic in the active region of the semiconductor device, boron, the concentration of the dopant such as phosphorus, is usually in the range of ^{10 15 / cm 3 ~10 20 /} cm 3. To predict device behavior and control manufacturing processes, 10
It may be necessary to control the variation or profile of the dopant with a lateral resolution of nm and a vertical resolution of 2 nm to 3 nm. However, currently known dopant profilers cannot provide this high accuracy in at least all three dimensions.

Known techniques for dopant profiling include S.
J. Elector by T. Ahn and WA Tiller
Chem. Soc. 135 (1988), J. Vac. Sci. Technol. B10 by H. Cerva, described in J. Vac.
(1992), p.491, p.491, selective etching of dopant density by transmission electron microscopy (TEM), for example, "VLSI Technology" by SM Sze, McGraw-Hill Book C
o., New York, 1983 (especially Chapters 5 to 10), secondary ion mass spectroscopy (SIMS), spreading resistance (S
R), macroscopic capacitance-voltage (CV) measurement. Another method currently under development is LP Sadwick.
J. Vac. Sci. Technol. B10 (1992), p. 468, by Dopant Density Selective Etching by Scanning Tunneling Microscopy (STM), HE Hessel et al.
J. Vac. Sci. Technol. B9 (1991), Planar STM described in p. 690, and JM Halbout and M.
J.Vac.Sci.Technol.b10 by B. Johnson
(1992), section STM described on page 508. While useful in certain aspects, these techniques have some drawbacks: they are destructive or require careful sample preparation, and have limited lateral resolution or dopant sensitivity.

One of the latest methods for determining dopant concentration is the scanning capacitance microscope described in U.S. Patent No. A5065103. It has the features of a scanning probe microscope and conventional CV technology. However, even a scanning capacitance microscope does not provide sufficient lateral resolution required in the future. In addition, lock-in techniques are used to reduce noise due to stray capacitance, thus slowing the scanning process, and high throughput with this method is unlikely to be realized.

Another method described in U.S. Pat. No. A5267471 uses a cantilever having two different mechanical resonance frequencies. When the device is used as a capacitance sensor, a portion of the resonant frequency is applied to the cantilever, and the movement of the cantilever is monitored by a laser interferometer and subsequent lock-in amplifier. As mentioned above, the use of lock-in amplifiers severely limits the bandwidth of the measurement.

The principle of a scanning probe microscope based on electromagnetically induced harmonic generation (SHM) is described in, for example, GP Kochanski (Ko
chanski), Phys. Rev. Lett. 62 (1989), No. 19, p.
Ult by W. Seifert et al.
ramicroscopy 42-44 (1992), pp. 379-387, Rev. Sci. Instrum. 63 (9), by B. Michel et al.
In September 1992, pp. 4080-4085, SJ Strnic (Str
anick) and PS Weiss, Rev, Sci. Inst
rum.64 (5), May 1993, pp.1232-1234. In the SHM technique, electromagnetic fields from the radio frequency (RF) to the optical frequency are transmitted through a conventional scanning tunneling microscope (ST).
M) Add to the tunnel gap. Higher frequencies (harmonics) are created by some electrical properties of the tunnel gap, which may be due to the non-linearity of the current-voltage curve or space charge effects. By using these harmonics as feedback for the STM chip positioning device, the insulating film and the semiconductor can be scanned. However, this feedback loop does not work on the conductor surface and the fragile tip hits the surface and breaks. This misconception prevents the SHM from being used extensively as an instrument for dopant profiling, as conductive regions appear regularly on the integrated circuit.

Accordingly, it is an object of the present invention to provide a device for determining cantilever deflection which is particularly suitable for cantilevers having small dimensions and therefore a very high resonance frequency, with regard to the above limitations of the art. It is another object of the present invention to provide a non-destructive method and apparatus for determining material properties, particularly dopant profiles, with a resolution scalable to 100 nm and below. The method and apparatus are equally applicable to both conductive and non-conductive surfaces. Another object of the invention is to increase the bandwidth of the runout measurement for known devices.

Summary of the Invention The above and other objects and advantages are achieved in accordance with the principles of the present invention as set forth in the appended claims.

Thus, in a basic variant, the device according to the invention comprises a flexible cantilever and a voltage which applies a DC voltage between the sample and the "piggybacked" reference surface or tip and the cantilever to be investigated during operation of the device. It has biasing means, antenna means for receiving radiation in the MHz and / or GHz range, and amplifying means designed to operate in this frequency range.
Due to the non-linearity of the resistance-voltage or capacitance-voltage characteristics of the interface between the cantilever and the second surface, radiation exiting the interface is not only at one (fundamental) frequency, but also at higher frequency components at the same time. And so-called harmonic signals. In principle, all components of these harmonics can be used, but in some embodiments of the present invention, as described below, the harmonic signal,
In particular, it is advantageous to use the second and third harmonic signals for measurement. A preferred range of frequencies is 100 MHz to 100 GHz, the lower limit being set by the efficiency of harmonic generation,
The upper limit is determined by the currently available high frequency signal generation and detection equipment.

In order for harmonics to be generated, usually a cantilever and
The sample or "piggyback" surface or the second surface, which is the surface of the chip, must form an interface consisting of a semiconductor or non-conductor boundary and a conductor boundary.
However, it has been found that the sensitivity of the device according to the invention supports embodiments in which both surfaces consist of semiconductor material. Thus, the device exhibits high efficiency in generating harmonic signals, independent of the nature of the second boundary.
Another advantage of the present invention is that a constant DC bias voltage can be selected without the need for re-examination, for example, when different surface materials are encountered during cantilever scanning.

The two boundaries are preferably separated by 0.1 nm to 100 nm. A DC voltage can be applied to this interface by using voltage bias means. Next, since the capacitance-voltage characteristic of the interface is non-linear, the oscillation of the cantilever causes the emission of an electric field signal oscillating by the resonance frequency and its harmonics. The radiated electric field is detected by an antenna and preferably by an amplifier or cascaded amplifiers and filters that make up a spectrum analyzer.
A change in force acting on the tip of the cantilever, and thus a deflection of the cantilever, can be detected as a change in the frequency of the electric field signal or a change in the amplitude of the vibration of the cantilever.

For example, by adding the output signal of the amplifier to feedback means for controlling the positioning means, such as a piezoelectric precision positioning system known in the art, the basic variant of the invention can be extended to a runout detection control device,
It becomes possible to control the position of the cantilever with atomic accuracy. This embodiment of the invention is particularly suitable for cantilevers having a resonance frequency above a few hundred MHz. Such cantilevers are too small to converge light well, and the amount of light reflected by the cantilever is below the current detection threshold, so known optical techniques such as beam deflection and interferometer usage Can not be used for

As described with respect to U.S. Patent No. 4,724,318,
It is known in principle to detect the deflection of an AFM cantilever using a "piggybacked" scanning tunneling microscope (STM). However, it is clear that the differences in the present invention provide several advantages. To detect tunneling current, the tip needs to be closer than 1 nm behind the lever. This close distance causes a large damping and is not practical when measuring large forces and force gradients, i.e. large swings. Another reason that has prevented the use of this method in commercial AFM microscopes is that the tunnel gap is not stable under ambient conditions. With the device of the present invention, the gap width can be increased up to 50 nm. The attenuation of the silicon cantilever is reduced, and the measurement sensitivity of the runout can be maintained at an extremely high level. Furthermore, the new device does not have the stability problem characteristic of AFM due to the detection of the tunnel current of the deflection. Furthermore, it can be carried out on a surface covered with a layer of an insulator such as an oxide or a nitride.

Embodiments of the present invention can be applied to any existing type of cantilever without the need for precise adjustment or replacement of the cantilever itself. It has been found that the device according to the invention has a good signal-to-noise ratio and therefore does not require a lock-in amplifier, thereby increasing the bandwidth of the swing measurement.

Obviously, the scope of the invention is not limited to a simple beam cantilever with one support. For example, the present invention can be easily applied to a cantilever having a complicated design such as a spiral shape having a plurality of support points.

Yet another embodiment of the present invention relates to an antenna for receiving an electric field radiated from an interface. The antenna may be a discrete conductor element or an integral part of a cantilever, sample support or piggyback element. In the latter case, means are provided to separate the bias voltage and other low frequency components from the high frequency signal, such as a "biased T" connector. This antenna may also be tuned, preferably tunable, as described, for example, by B. Michel et al., Rev. Sci. Instrum. 63 (9), September 1992, pp. 4080-4085. It can be incorporated into a simple cavity. Most of the signal output can be detected by using the cavity and tuning the cavity to the frequency of the signal. Without cavities, high flexibility in measurement and instrument design is obtained. However, in this case,
By using specially designed high impedance filters and amplifiers, the loss of sensitivity can be compensated.

Certain aspects of the invention are directed to investigating foreign surfaces,
Especially for probing advanced integrated circuits, i.e. for dopant profiling, use is made of an apparatus comprising a flexible cantilever as described above and means for detecting harmonic electrical signals.

It is well known that the electrical signal emitted from the gap between the chip and the sample depends on the material that bounds the interface. However, there are no well-known instruments that are flexible enough to handle the complex surfaces found in ICs, and the introduction of a suitable dopant profiler has failed. Scanning capacitance microscopes can, in principle, scan across any surface, but have been unable to maintain high resolution under any such surface conditions. The present invention solves this problem by using a device operable in atomic force mode to detect cantilever deflection by any of the aforementioned methods, while simultaneously detecting the electrical signal emitted from the gap region. Enable.

Another embodiment further includes means for generating an oscillating electric field and coupling means for applying the electric field to the cantilever. In this embodiment, the frequency that modulates the gap between the cantilever tip and the sample surface is not determined by the resonance frequency of the cantilever, but can be adjusted to a predetermined value. This value depends on the structure and composition of the sample surface to be investigated. It is preferred to use radio frequency or microwave frequency electric fields. This embodiment is further improved by providing appropriate filter means to separate the fundamental frequency obscured by an externally supplied signal from its harmonics.

In a modification of this embodiment, the amplitude and vibration frequency of the cantilever are controlled by using an externally supplied oscillating electric field. This control is particularly efficient when the externally supplied electric field is tuned to the resonance frequency of the cantilever. The same effect can be achieved when the piezoelectric element or the piezoresistive element constituting a part of the cantilever body is excited by an externally supplied electric signal to cause the cantilever to vibrate. Another alternative to causing vibration is to provide a sufficient amount of thermal energy to the cantilever, in which case a bimorph structure containing materials with different coefficients of thermal expansion must be provided. Heat supply to the cantilever can be enhanced by incorporating a suitable heating element into the cantilever structure.

In another embodiment of the invention, the chip is attached to means for measuring the current flowing through the gap between the chip and the surface. This allows the known (DC) tunneling current to be determined from the STM described above, or tunneling to and from the surface to be investigated under the influence of an applied AC field, as described by Kochanski. An alternating current resulting from a small number of electrons can be determined. The latter case also applies to insulators.

Both currents can be used as input signals to the feedback loop of the positioning device, and the operator of the device according to the invention can take two to four different ways to control the gap width between tip and sample. it can.

In certain preferred embodiments of the present invention, the force sensor tip and cantilever are coupled to the atomic force cantilever by a conductive cladding or coating. The cladding is formed by suitable deposition techniques well known in the art.
Can attach to normal AFM cantilevers. With this chip integrated structure, a conventional scanning harmonic microscope (SH
The technical overhead is significantly reduced compared to devices that have to use atomic force sensors parallel to the (metal) chip of M).

It is immediately possible to use this signal detection on an array of cantilevers tuned to slightly different resonance frequencies. The deflection of each cantilever can be achieved by selectively coupling an input DC voltage or input electromagnetic wave to each of these cantilevers, or by tuning a frequency detection device to its resonant frequency.

For example, in the case of the known scanning surface harmonic microscope, J.-
By P. Bourgoin et al. (International Conf.
erence on Micro− and Nano−Engineering MNE '94, Da
vo, Switzeland, September 26-29, 1994), the efficiency of the apparatus can be further increased by utilizing the enclosed chamber and means for controlling the humidity in the interface region. When the humidity is set to an appropriate value, droplets are formed in the interface area, which concentrates the electric field in this area.

These and other novel features which are believed to be characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as the preferred mode of use, as well as its objects and advantages, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings.

Description of the drawings The present invention will be described in detail with reference to the following drawings.

FIG. 1 is a diagram showing a model of a gap between a chip and a sample.

FIG. 2 is a view showing a first embodiment of a shake sensor according to the present invention.

FIG. 2B is a diagram showing an ESR measuring device including a second embodiment of the present invention.

3A and 3B are views showing still another modification of the shake sensor according to the present invention.

4A, 4B, and 4C illustrate the use of the present invention as a device for surface investigation according to various embodiments.

 FIG. 5A and FIG. 5B are diagrams showing experimental results.

6A, 6B, and 6C are diagrams showing still another experimental result.

Next, referring to FIG. 1, an RC parallel circuit 1 will be described as a model for facilitating understanding of generation of harmonics in an interface or a gap separating a cantilever and a second surface.
Is shown. The RC parallel circuit 1 is an electric model of this gap, and a DC voltage is applied. An input microwave signal ω generated by a microwave generator (not shown) is coupled to the gap, for example, via a tip or a sample holder. The input microwave signal has a frequency ω. The radiation exiting the gap contains a component having a harmonic frequency nω. These components are the resistance R
(V) or the nonlinearity of the capacitance C (V).

Next, referring to FIG. 2A, a basic modification of the present invention is schematically shown. A flexible cantilever 220 with a tip on the tip and a sample holder 230 with a sample 231 are connected to a DC voltage source 250, which provides a bias voltage on both sides of the interface. Because the cantilever vibrates at the resonance frequency or the frequency of the externally supplied signal, the gap between the tip and the sample is modulated, emitting electromagnetic waves including signals at the fundamental frequency ω and the harmonic frequency nω. These signals are received by the antenna 261 and amplified by the microwave amplifier 260 for the next processing (display, control, etc.).
This simple variation of the invention is particularly important in creating large arrays of cantilevers. Each cantilever of the array can be tuned to a different fundamental frequency. Next, using a spectrum analyzer to separate the contribution of each cantilever to the detected signal, the deflection of each cantilever in the array can be easily observed.
In this basic variant, the excitation energy required to balance the energy dissipation of the cantilever must be provided externally, for example by heating or radiation. When an electromagnetic wave is not supplied from outside, it is desirable to provide a cantilever having a high resonance frequency. 0.01GH
A cantilever that resonates at a frequency of z to 1.0 GHz is a bin (B
inh) et al. from Surface Science 301 (1994), L224.

FIG. 2B shows the means by which electromagnetic radiation 240 causes lever resonance from the outside. A device for measuring the electron spin resonance (ESR) of a sample is shown, which is described in Nature 360,563 (1992) by Rugar et al.
By detecting the harmonics created in the gap between the cantilever 232 supporting the ESR sample and the second (reference or "pibby back") surface comprising the metal tip 222, The difference is that the shake is detected. High frequency coil 240, magnet 291 and sweep coil 292 are standard components of an ESR measurement device. Modulation of the magnetic field at the sample results in oscillation of the cantilever, typically about 1 nanometer in amplitude, which is detected as a change in the harmonic signal. This signal occurs in the gap between tip 222 and silicon cantilever 232. The signal generator 293 sweeps the magnetic field to resonate the spin at an applied high frequency of half the resonant frequency of the cantilever. The detection circuit 262 is tuned to a harmonic of this resonance frequency.

Another variation of the present invention is shown in FIG. 3A. In this example, the microscope has, in particular, a cantilever 320 made of a semiconductor material 321 connected to a microwave power supply 340, the back side of which faces the metal chip 323. Tip 323 and cantilever 32
DC voltage is applied to 0. This voltage can be adjusted to a value suitable for the material of the cantilever. further,
Fixing means (not shown) are provided to keep the distance between the tip and the cantilever at a default value of 50-100 nm. This gap width is sufficiently larger than the distance at which electron tunneling occurs, that is, US Pat.
Note that it is much larger than the piggyback STM described in 724318. In addition, the gap width is set between the tip 323 and the cantilever 3 under normal conditions.
There is no need to provide a chip with a positioning system that is large enough to prevent 20 collisions and thus controlled by a separate feedback loop. On the other hand, in order to implement this variant of the invention in a mode generally known as "constant force mode" in the field of force scanning microscopes, an integrated circuit 371 for controlling the sample positioning means 331 comprises a feedback loop 370. Provided as part.

Further, in the above-described variant, an external microwave signal is sent via the tip 323 to the gap between the tip and the cantilever. The input microwave signal source 340 has a bias T34
1 connects to the DC voltage circuit. The emitted radiation ω and nω are received by the antenna 361. The amplifier circuit includes a preamplifier 362 having a bandwidth in the range of 1 GHz to 4 GHz and an amplification factor of 40 dB, and a band filter 363 (2.1 GHz to 3.5 GHz) for removing noise and unnecessary frequency components from the signal. The next spectrum analyzer 364 produces a frequency resolved representation of the signal. Alternatively, the output of the spectrum analyzer can be used as an input to integrated circuit 371.

In yet another embodiment of the present invention, a device that includes a microwave source, an antenna, an amplifier, and a feedback circuit and that can be connected to a known atomic force microscope (AFM) can be created. The deflection of the AFM cantilever is ST
It can be detected with an accuracy of about 10 picometers without causing stability problems that have hindered the use of M-based detection methods.

FIG. 3B shows a compact design according to the invention, in which the additional metal tip has been replaced by a metallization 322 of the cantilever 320. In addition, the output of spectrum analyzer 364 provides two feedback loops 370, 35
Connected to the input of a phase motivation loop (PLL) 372 which forms part of zero, the feedback loop 370 is locked to the resonant frequency of the cantilever. This loop includes an adder 374 and is used to electrostatically cause the cantilever 320 to vibrate. Since the PLL responds to the frequency shift of the signal, the illustrated device can be used to measure the attenuation of the cantilever oscillation. After further smoothing the RMS (root-mean-square) output of the PLL by the integrator 373, it can be connected to the positioning means 331 of the sample holder 330 as a control signal to keep the attenuation constant.

Referring now to FIGS. 4A, 4B, and 4C, a variation of a surface inspection tool, such as a dopant profiler, according to the present invention is shown. The first modified example shown in FIG. 4A is a modified example of the present invention caused electrostatically as described above (FIG. 3A), and includes a switching means 475. When the switch is in position 1, harmonic detection is used to control runout. On the other hand, at position 2, the microwave source is the cantilever 42.
Connected to the gap between zero and sample holder 430 to allow for dopant profiling. Also, the second
May be provided to the second microwave source. Utilizing this particular embodiment, detection of cantilever deflection and inspection of the sample surface are possible at the same time.

For the above example, the dopants of FIGS. 4B and 4C
The profiler includes additional means for detecting cantilever deflection, said means being based on a method whose principle is known and partially described above. Examples of measuring the deflection of a cantilever by a piezoresistive method (FIG. 4B) or by a beam deflecting device that measures the intensity of the laser beam reflected at the back of the cantilever (FIG. 4C) are shown. However, any other known shake detection method may be used instead.

In either embodiment, the metallization 4 of the cantilever 420
22 is connected to the current / voltage converter 490 to operate the cantilever in the STM mode. At this time, switch 476
Includes a feedback circuit 470 that can automatically select various input signals. For example, if you know the exact topology of the sample, as in the case of IC manufacturing,
The switch can be programmed or controlled by an external device. Alternatively, the shake is monitored with at least a second shake detection method that is parallel to what is currently providing the input signal to the feedback circuit 470. In the latter case, the switch
476 automatically changes its position when the current applied signal deviates significantly from its expected value.

The two variants shown in FIGS. 4B and 4C differ in the way they receive radiation emitted from the gap,
The illustrated embodiment includes a tunable cavity 465, for example, as described by Michael et al., Which allows for pre-selection of signal frequency, sensitive detection of signals, and sensitive detection of radiation in a narrow bandwidth. It is. In this embodiment, it is preferable to use a shake measurement method that does not interfere with the characteristics of the cavity as the resonator. Therefore, the piezoresistive layer 423 is incorporated in the cantilever body 420. Piezoresistive element measures the resistance and cantilever 420
Wheelstone bridge arrangement 48 to find runout
This is the main part of 0. It can be replaced with a piezoelectric element that generates a voltage in accordance with piezoresistance running and bending of the cantilever.

In the embodiment of FIG. 4C, no cavities are used, and the antenna is formed with the conductive coating 422 of the cantilever. The input path and the output path of the high-frequency signal are separated from the DC circuit 450 by the bias T elements 441 and 466. As described above, a wider range of different runout measurement methods can be used due to the lack of cavities. In the illustrated embodiment, the intensity of the reflected laser beam 482 is measured, and this intensity changes as the cantilever 420 bends.

Combining the various elements of the previous embodiments, in particular selecting a particular method of coupling the input signal to the gap and coupling the output signal to the amplifier cascade, replacing the conductive coating of the cantilever with a cantilever made of a conductive substrate, Alternately, replacing the coating with a piggyback tip as shown in FIG. 3A is a task that would be obvious to one skilled in the art.

As mentioned above, the new microscope according to the invention is advantageously used for characterizing the surface of integrated circuits (ICs). FIG. 5 shows the results obtained by examining a sample of n-type silicon doped with boron ions. FIG. 5A shows a sample structure consisting of alternating stripes of n-doped silicon and p + -doped silicon. Each stripe is about
It has a width of 10 μm. Such a lattice is found in a manner similar to the source / channel / drain regions of a PMOS device. In FIG. 5B, the intensity of the second harmonic signal is shown as a function of tip position and bias voltage along a line extending perpendicular to the n-doped and p + -doped stripes. Line scan is -1.45V (a), -0.55V (b) and 1.2V
(C). For the sake of clarity, the starting point of the curve is shifted, and the curve b is magnified five times. These scans can be used to distinguish high-concentration dopant regions from low-concentration regions or depletion regions. FIG. 6 shows the results obtained by examining a sample doped with arsenic (n +). 1.15V (a), -1.15V (b) and -1.50
Line scans, each performed at a bias voltage of V (c), clearly show a lateral dopant profile. The maximum amplitude is much higher in the lightly doped region than in the heavily doped region. The resolution obtained is less than 35 nm. By controlling the humidity inside the microscope, the resolution can be increased. The simultaneously recorded line scan (d) shows the physical height of the sample measured by the STM and AFM operating modes of the microscope. The measured values are plotted in a three-dimensional plot (FIG. 6C) having a horizontal axis with the bias voltage in volts and the position in nanometers. The vertical axis shows the second harmonic signal in nanovolts (nV).

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michel, Bruno Gatticon, Switzerland, Optostall Tenvark 13 (56) References JP-A-4-361110 (JP, A) JP-B-6-103176 (JP, B2) A . S. Hou et. al, "PI COSECCON ELECTRIC L SAMPLING USING A SCANNING FORCE MI CROSCOPE", ELECTRON ICS LETTERS, (UK), 1992.12.03, Vol. 28, No. 25, p. 2302-p. 2303 W. Krieger et. al, "Generation of microwave radiation in the tunneling job of a scanning tunneling microscope," Physical Review, B. (1990), Physical Review B (CONTENS. RESERV. 41, No. 14, p. 10229-p. 10232 (58) Field surveyed (Int. Cl. ⁶ , DB name) G01N 37/00 G01B 21/30 JICST file (JOIS) ["A FM" + "Atomic force microscope"] * "Harmonics"

Claims (14)

(57) [Claims] (A) means for applying a DC voltage to flexible cantilevers (220, 232, 320, 420) of an atomic force microscope; (b) high-frequency electric signals are applied to the flexible cantilevers. High-frequency electric signal applying means (240, 340, 440) for applying the applied electromagnetic wave to start the oscillation of the cantilever and emitting an electromagnetic wave; (c) antenna means for receiving the electromagnetic wave (261, 263,
(D) amplifying means (260, 26) connected to the antenna means;
2, 362 to 364, 462 to 464) for measuring the force applied to the flexible cantilever of the atomic force microscope or the deflection thereof. 2. The apparatus according to claim 1, wherein said high-frequency electric signal applying means applies said high-frequency electric signal to a gap between said cantilever and a sample. 3. The high-frequency electric signal applying means applies the high-frequency electric signal to a gap between the cantilever and a metal chip (323) provided on a rear surface of the cantilever. An apparatus according to claim 1. 4. The apparatus according to claim 1, wherein said amplification means detects a high frequency (nω) of said electromagnetic wave (ω). 5. Apparatus according to claim 1, wherein said amplifying means operates at a frequency in the range of 10 MHz to 100 GHz. 6. The apparatus according to claim 6, wherein said sample is a sample holding means.
3. The apparatus according to claim 2, wherein at least one of the cantilever, the sample holding means and the tip (323) forms part of the antenna means. 7. The apparatus of claim 1, further comprising a cavity (465) having a conductive wall surrounding the cantilever (420), wherein one of the walls is movable relative to the other. The described device. 8. The method according to claim 8, wherein the cantilever is made of a conductive material (322, 4).
22. The device according to claim 1, comprising the coating of 22). 9. A piezoelectric actuator for controlling the distance between the cantilever and the surface of the sample, a force detecting means for measuring the deflection of the cantilever, and a switching feedback means for controlling the actuator. 470), wherein the feedback means comprises:
2. The apparatus of claim 1, wherein said apparatus is switchable to the output of said force detection means or amplification means and serves as a dopant profiler. 10. Means (490) for detecting a tunnel current between the cantilever tip and the sample,
The apparatus according to claim 9, wherein the feedback means is switchable to an output of the tunnel current, the force detection means, or the amplification means. 11. A screen for applying a DC voltage according to claim 1, a high-frequency electric signal applying means, an antenna means, and an amplifying means, and further processing a measured force or shake signal to display the image. A sample analyzer comprising: means for positioning a sample for display; and means for permanently storing a processed force or deflection signal on a magnetic medium. 12. A DC voltage is applied to flexible cantilevers (220, 232, 320, 420) of an atomic force microscope,
Applying a high-frequency electric signal to the flexible cantilever to start oscillation of the cantilever and emit an electromagnetic wave; receiving and amplifying the electromagnetic wave; and changing the frequency or the amplitude of the received electromagnetic wave. Determining the force applied to the flexible cantilever of the atomic force microscope or the deflection thereof. 13. The method of claim 12, wherein said high frequency electrical signal is applied to a gap between said cantilever and a sample. 14. The cantilever and a metal chip (32) provided on a back surface of the cantilever, wherein the high-frequency electric signal is transmitted to the cantilever.
13. The method according to claim 12, wherein the voltage is applied to the gap between 3).