JPH0269643A - Surface analysis instrument - Google Patents

Abstract

PURPOSE:To measure the spectroscopic absorption characteristics of a sample surface with resolution of 0.1mum by measuring the spectroscopic absorption characteristics of a minute part by detecting the height variation of the sample surface when the surface is irradiated with radiation by using a probe. CONSTITUTION:When a metallic probe 12 is brought nearer to a sample 11 to be inspected of a conductive material to a distance of about 1nm while a voltage is applied across the probe 12 and sample 11, a tunnel current flows between the probe 12 and sample 11. The tunnel current is sensitive to the variation of the distance between the probe 12 and sample 11 and changes by one figure against a distance change of 0.1nm. When the sample 11 is inspected with a scanning tunnel electron microscope, the surface of the sample 11 is scanned with the probe 12 by using a fine adjustable mechanism 20. While the scanning is made, an adhering matter 13 absorbs radiation 40 by an absorption coefficient corresponding to the wavelength of the radiation 40 and swells. As the matter 13 swells, the distance between the probe 12 and matter 13 becomes shorter and the tunnel current increases. Therefore, the probe is raised until the current value reaches the original value. On the contrary, the probe is lowered to a recessed part. By repeating operations and showing the voltage fluctuation applied to the mechanism 20 in the form of a picture, the surface rays of light of the sample 11 are observed in the scale of atoms.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to the qualitative and
The present invention relates to a surface analysis device that is effective for quantitative analysis, and particularly to a surface analysis device that is very effective for failure analysis of semiconductor integrated circuit devices and the like.

(Prior Art) Infrared absorption spectroscopy and visible absorption spectroscopy make it possible to measure interatomic vibrations and electronic transitions specific to individual substances, and are widely applied as analysis methods.

By the way, in the manufacturing process of semiconductor integrated circuit elements and the like, evaluation of thin films formed on semiconductor surfaces and analysis of impurities attached to the surfaces have become important issues. Several efforts have been made to apply the above spectroscopy to such local analysis.

For example, Q,3erres 5(ApD3pectr
osc Toyu 1000.1987> attempts to focus infrared light and open up local infrared absorption spectroscopy. However, because the wavelength of infrared rays is relatively long, the spatial analysis ability is only 10μ.
It remains at around m.

On the other hand, the higher spatial analysis ability is 1! '7 In order to
A method of estimating the absorption coefficient by measuring the temperature rise of a sample due to infrared light irradiation, for example, MarcA.

Taub Onb I alt, App +, ph
ys.

1ett, 52) has been reported. This hand) person J3
Now, an interference microscope with visible light as a light source is used to detect thermal expansion due to temperature rise as positional changes on the sample surface.

The analytical ability of about 1 μm, which corresponds to the spatial analytical ability of the optical microscope used for the measurement, is shown in blue.

(Problem to be Solved by the Invention) However, the line width of current semiconductor integrated circuit elements has reached 1 μm or less, and for evaluation, it is necessary to
．． A resolution of about 1 μm is required.

The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a surface analysis device having local absorption spectroscopy capability and spatial analysis capability of 0.1 μm or less.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides fine movement means for bringing a probe close to the surface of a sample to be inspected for measuring the height of the surface of the sample to be inspected; An irradiation means for irradiating monochromatic radiation to a portion of the surface of the test sample facing the probe; It is detected as a change in height, and it is detected! The above object is achieved by including a control means for measuring local spectral absorption characteristics for 8FA.

(Function) By irradiating the surface of the specimen to be inspected using visible light or infrared light as the Q=J ray, the expansion and contraction of the sample due to temperature changes between the irradiated area and the surface of the specimen to be inspected when not irradiated is suppressed. It is detected as a height change on the surface, and the local spectral absorption characteristics for the (l)-1 radiation are measured.

Here, position fluctuations can be measured by measuring the tunnel lightning current flowing between the sample and the probe, or by using a sensor that detects fluctuations transmitted to the probe via atomic force moving between the probe and the sample. Use a method that As a means for detecting this positional variation, a method using the same principle as a scanning tunneling electron microscope (STM) or an atomic force microscope can be used.

The detection sensitivity in the height direction of position fluctuation measurement using a probe is 10'.
The horizontal analysis ability is about iQ nm.
The resolution of local analysis is extremely high.

For example, when a minute substance with a high absorption coefficient is attached to a substance with a relatively low radiation absorption rate, such as silicon, it is possible to substantially measure the absorption characteristics of only the attached substance.

This is extremely effective especially for identifying impurities adhering to the surface and for constant analysis during the manufacturing process of semi-19-dimensional devices.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention. Before that, the structure of a scanning tunneling electron microscope m (STM) will be explained with reference to FIG. 6.

In FIG. 6, J3 indicates a specimen to be inspected, 12 indicates a probe of all types, and 2o indicates piezoelectric elements 21, 22, . . . in each direction of X, Y, and Z.
23 is a fine movement mechanism, 31 is a control shield, 32 is an X-Y drive circuit, 33 is a Z drive circuit, 34 is a tunnel current detection circuit, 35 is a lens, and 36 is a display.

In this configuration, when a voltage is applied between the conductive material sample 11 and the metal deep needle 12 and the sample 11 is brought close to a distance of about 1 m, a tunnel current flows between them.

This current is sensitive to distance changes between the two, and is 0.1
The tunnel current changes by one order of magnitude for a distance change of 1 nmV.

In STM, the probe 12 is scanned along the surface of the sample 11 while keeping the tunneling current constant using the fine movement gate mechanism 20. When the probe 12 comes to the white part of test F111, the tunnel current increases, so raise the probe 12 until the current returns to the original value, and conversely lower the probe 12 at the concave part. By repeating this operation, the microtremor extracts the voltage change applied to the structure 20, converts it into an image, and observes the surface optical image of the sample 11 to be inspected on an atomic scale.

By utilizing the fluctuations in the tunnel current between the probe 12 and the sample to be inspected 11 in this way, positional fluctuations can be detected with high analytical ability in both the vertical and horizontal directions.

Kimitsuaki proposed that the fluctuation of the tunnel current be determined by holding the probe 12 in a fixed position and irradiating the Q = 1 ray in a pulsed manner, or by determining the fluctuation of the tunnel current even when irradiating the Q = 1 ray. By moving the probe 12 up and down using a micro-movement blur in the Z direction so that the value remains constant, and by extracting the voltage change at that time, the amount of thermal expansion due to temperature change due to radiation absorption of the sample can be reduced to 10'nm.
It is measured with the following analytical ability. Furthermore, the local spectral absorption characteristics of the surface of the sample 111 are measured by illuminating Q=1 while sweeping the wavelength of the incident pulsed radiation. Furthermore, for an insulating sample to be inspected, the spectral absorption characteristics were measured by detecting fluctuations in the atomic force acting between the probe 2 and the sample.

The embodiment shown in FIG. 1 will be described with the above in mind.

In FIG. 1, 11 is a sample, and a metal probe 12 is placed close to the surface of this sample 11. The probe 12 is attached to a fine movement gate mechanism 20 consisting of piezoelectric elements (actuators) 21 and 22 (not shown) 23 that enable fine movement in each of the X, Y (not shown), and Z directions. This fine movement gate structure 20 is attached to a gate structure (not shown). Incidentally, the coarse movement mechanism moves the fine movement gate structure 20 to which the probe 12 is attached, and has a mechanism for bringing the probe 12 sufficiently close to the surface of the sample 11.

The piezoelectric elements 21 and 22 are driven by an X-Y drive circuit 32 controlled by a calculation controller 31, and the probe 12 is driven to scan in the in-plane direction of the surface of the sample 11. Also,
The piezoelectric element 23 is driven by a two-axis drive gripping mechanism 33 controlled by a calculation animal 31, and this drive causes the probe 12 to move up and down perpendicular to the surface of the sample 11. Further, the diffraction grating 42 and the shutter 43 are controlled by the meter 31.

A predetermined voltage is applied between the sample 11 and the probe 12, and a tunnel current detection circuit 34 is connected to detect the current flowing between the two.

On the other hand, the sample 11 is placed on an X-Y stage 14 that can be roughly moved in the X-Y direction.

The embodiment shown in FIG. 1 is for measuring the absorption characteristics of minute deposits 13 on a sample 11 that is almost transparent to the 9A line, and the radiation 40 is irradiated from the back side of the sample to be inspected. be done.

Next, the irradiation system for Q=1 line 40 will be explained. light source/
As 11, continuous wavelength light from a synchrotron radiation light source is used. After the radiation 40 is made monochromatic by a diffraction grating 42, a shutter 43 for performing pulsed irradiation;
After passing through a filter 44 that blocks harmonic light,
After the light is focused by the lens 45, it is irradiated onto the deposit 13 on the sample 111 to be inspected. Here, as illustrated, the beam diameter of the radiation 40 is smaller than the diameter of the deposit 13, but it is also possible to analyze deposits smaller than the beam diameter.

Next, a method for measuring the radiation absorption characteristics of deposits using this apparatus will be described with reference to FIG. 2.

FIGS. 2(a), (b), and (c) show the channel current, the timing of opening and opening of the shutter 43, and the wavelength of the radiation 40 separated by the diffraction grating 42 as functions of time, respectively. . Although the wavelength of the radiation 40 changes continuously over time, the shutter 43 is heard at time t1''C'' and the shutter 43 is closed at time t2. Meanwhile, the deposit 13 has an absorption coefficient corresponding to the wavelength of the radiation 40)
It absorbs the line 40 and the temperature rises. Accordingly, the kimono 13 undergoes volumetric expansion. As a result, the distance between the probe 12 and the top of the deposit 13 becomes shorter, and the tunneling current increases. The degree of increase in this tunnel current reflects the average absorption coefficient between wavelength λ1 and wavelength λ2. If this measurement is repeated while sweeping the wavelength further and the envelope of the tunnel current is traced, a peak corresponding to the peak of the absorption characteristic will appear.

Next, an example of actually analyzing deposits on a wafer using this method will be described. FIG. 3 shows a cross-sectional view of the sample 11 to be inspected. Here, a silicon wafer was used as the sample to be inspected, and a thin line of PMMA (polymethyl methacrylate), which is an electron beam resist, was formed on the silicon wafer as a garment 13 by electron beam drawing. Line width is 0.5
The μm1 height is 0.5 μm. In addition, in order to impart conductivity to the surface, a gold evaporated film 15 was deposited on the entire surface of the sample 11 at a temperature of 0°1.
It was formed with a thickness of μm.

The radiation obtained by analyzing the infrared light absorption characteristics of this test sample 1 using the @i setting in FIG. The half width of lJ 40 is 10-1
cm and intensity 1,11 mwT - about 5 μffl'
17) The light was focused on a specific area. In addition, the pulse interval is 1/100 seconds, the wavelength 8 pull speed is 10"cm/second,
Measurements were carried out in the range from 50Q-1cm to 1500-1cryl). As a result, the tunneling current increased up to three times at wavelengths corresponding to natural frequencies such as C-0 stretching vibration and C-0-C bending signal specific to the ester group of PMMA.

In addition, 500 to 60, which does not correspond to the absorption peak of PMMA,
The variation in tunnel current near 0''cm was less than 10%.

As described above, by using the apparatus of this embodiment, it is possible to accurately measure the radiation absorption characteristics of deposits of 1 μm or less attached on a substrate.

FIG. 4 is a block diagram showing a second embodiment of the present invention. This embodiment has the same sample portion, drive vJ mechanism 20, and control system as the first embodiment, but is characterized by using a Michelson type interferometer 46 instead of making the radiation 4o monochromatic. be. The Michelson interferometer 46 is composed of a half mirror 47 for dividing the optical path of the radiation 40, and two reflecting mirrors 48 and 49 that are perpendicular to each other. Reflector 4
8 is fixed, whereas the four reflecting mirrors are configured to be movable perpendicularly to the optical path.

Next, a method of measuring spectral characteristics using this interferometer 46 will be explained.

First, the probe 12 is brought close to the sample 11 to be inspected, and the tunnel current flowing between the two is measured. Next, the position of the reflecting mirror 49 is moved up and down, and while sweeping the optical path difference γ with the light reflected by the fixed reflecting mirror 48, the height 2 (
Δγ).

Here, in order to measure 2(Δγ), the relationship between the distance between the probe 12 and the sample 11 and the tunnel current is measured in advance.
The tunnel current may be monitored and estimated from its fluctuations, or a voltage may be applied to the Z drive circuit 33 so that the tunnel current is constant, and estimation may be made from the applied voltage.

Here, if the wavelength distribution of the light source is Io (λ), then the wavelength distribution of the radiation irradiated to the sample 11■○(λ0.γ)
has passed through the interferometer 46, so it can be expressed as 1o (λ, γ) = Io (λ) (1-e-2''T//') (1).

By the way, the fluctuation ff1dz(Δγ) is the light absorption coefficient S
The following relationship exists between (λ) and lo (λ, γ).

dz (γ) = A/lo (λ, △7)・S (λ) dz... (2) Here, A is a proportionality constant, and it is a constant of proportionality, and the shape of the sample, specific heat, size, heat transfer coefficient, etc. is a function of

Substituting equation (1) into equation (2), dz(γ) 1/Io(λ), S(λ)(1e−2πΔγ
/λ)dz -A(/Io(λ)S(λ)dλ fΣIo(λ)S(λ, e-2yrΔγ/λdλ)
... (3)
becomes.

Here, the first term on the right side corresponds to the height variation ΦdZ(○) when the optical path difference is Δ7-0. Therefore, equation (3) is dz (0)-dz (γ) = AJIo(λ)s(λ, e-2yrr/λdλ
...(4).

Here, if we set dz (0)-dz (7)=dZ (7), then dZ(γ)=Io(λ)s(λ)e-2y'rγ/λd
λ...(5).

When this is Fourier transformed, it becomes 10 (γ) S (γ) Af2π (6). Therefore, by measuring the change in the height direction tl[dz(γ) at a plurality of points while stirring and pulling the optical path difference γ, and performing Fourier transform on this, I.

(γ)S(γ) can be obtained.

Actually, series calculation is performed by approximating equation (6) with the following equation.

1o (γ)S(γ) (7) By measuring the wavelength distribution of the light source in advance and dividing Equation (7) by this, the absorption coefficient S(λ) can be determined. Note that these calculations are performed using the computer 31.

In this embodiment, since light of all wavelengths from the light source 1 is irradiated onto the sample 11 at once, the efficiency is high and spectral absorption characteristics with a large signal/M sound ratio can be measured in a relatively short time.

FIG. 5 is a diagram showing a third embodiment of the present invention.

In this embodiment, diamond is used as the probe 12, and it is connected to a fixing block 25 by a plate spring 24. A metal probe 26 is attached to the back surface of the leaf spring 24. The distance between the probe 12 and the sample to be inspected 11 is determined by the change in tunnel current between the plate spring 24 and the metal probe 26, which is transmitted to the leaf spring 24 by the repulsive force between the atoms that touch between them. detected. Further, the block 25 is fixed to a Z-fine shield structure 23 made of a piezoelectric element. The height direction detection device 27 has an X, Y, and Z gate structure as a whole (see 'Ill' in the figure).
) is installed. An n@ is attached to the sample 11 to be inspected, which irradiates the synchrotron radiation 40 from diagonally above. Its configuration and operation are the same as those described in the first embodiment, so their description will be omitted.

According to this embodiment, there is no need to coat the insulator with a metal film when measuring the insulator, so it is suitable for non-destructive testing. In addition, since the radiation 40 is irradiated from above the sample 11,
It is also possible to measure deposits on a sample to be inspected that is opaque to zero radiation.

Note that the present invention is not limited to the embodiments described above. For example, the light source for the light irradiated onto the sample 11 is not limited to synchrotron radiation, but is also a wavelength-tunable CO2
A monochromatic light source such as a laser or a laser beam such as a diode type semiconductor laser may be used. Further, any monochromatic continuous light source such as a thermal radiation type continuous light source can be used.

Furthermore, the radiation irradiation method may be pulsed or continuous.

Further, the side of the probe 12 that drives the probe 12 is not limited to one using a piezoelectric element, and may be of any type as long as it can move the probe with high resolution.

[Effects of the Invention] As explained above, according to the present invention, the group 1111 line can be illuminated with Q! Since the structure is configured to measure the spectral absorption characteristics of minute parts by detecting the height fluctuation of the sample surface during I L using a probe, the spectral absorption characteristics of the sample surface can be measured with a resolution of 0.1 μm or less. can be measured. In particular, the spectral characteristics in the infrared region are effective for identifying objects, so they are extremely effective for identifying impurities that adhere during the semiconductor device manufacturing process.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
FIG. 3 is a waveform diagram for explaining the operation of the embodiment shown in FIG.
5 is a block diagram showing a second embodiment of the present invention, FIG. 5 is a block diagram showing a third embodiment of the present invention, and FIG. 6 is a schematic block diagram of a scanning tunneling electron microscope. DESCRIPTION OF SYMBOLS 11... Sample to be inspected, 12... Probe, 13... Deposit, 14... X-Y stage, 15... Gold thin film,
20... Fine vJ mechanism, 21... X fine vJ mechanism, 22
...Y fine movement mechanism, 23...Z fine movement l! Structure, 24...
- Leaf spring, 25... Fixing block, 26... Metal probe, 27... Height measurement structure, 31... Calculator, 3
2...X-Y drive circuit, 33...Z drive circuit, 34
... tunnel current detection circuit, 40 ... radiation, 41
...Light source, 42...Diffraction grating, 43...Sissetta, 44...Filter, 45...Lens, 46...
Michelson interferometer, 47...half mirror...reflector with the same letter, 4...movable reflector. Figure 1 Figure 2 Figure 6

Claims (5)

[Claims] (1) Fine movement means for bringing a probe for measuring the height of the surface of the sample to be inspected close to the surface of the sample to be inspected, and a portion of the surface of the sample to be inspected that faces the probe is made monochrome. irradiation means that irradiates radiation, and detects expansion and contraction due to temperature changes on the surface of the sample to be inspected during irradiation and non-irradiation as changes in the height of the sample surface, and measures local spectral absorption characteristics for radiation. A surface analysis device comprising: a control means for controlling a surface; (2) The surface analysis device according to claim 1, wherein infrared light is used as the radiation and local spectral absorption characteristics are measured while sweeping the wavelength of the infrared light. (3) The surface analysis apparatus according to claim 1, wherein means for detecting a tunnel current flowing between the sample to be inspected and the probe is used as the means for measuring the height of the sample surface. (4) The surface analysis apparatus according to claim 1, characterized in that the means for measuring the height of the sample surface is a means for measuring the atomic force acting on the probe with respect to the sample to be inspected. (5) fine movement means for bringing a probe close to the surface of the sample to be inspected for detecting the height of the surface of the sample to be inspected; an irradiation means for irradiating radiation that has passed through the interferometer; and an irradiation means that irradiates the radiation that has passed through the interferometer, and while sweeping the optical path difference between the radiation reflected by the fixed reflecting mirror and the movable reflecting mirror of the Michelson type interferometer, height fluctuations on the surface of the sample to be inspected are detected. A surface analysis device comprising a means for detecting using a probe, and a means for determining local spectral absorption characteristics by calculating the optical path difference dependence of the height fluctuation detected by this means.