JPS6298208A - Surface roughness measuring instrument using electron beam - Google Patents

Abstract

PURPOSE:To measure the depth of projections and recesses of the surface of a sample quantitatively in the middle of an analysis of the sample by irradiating the sample with an electron beam and detecting its reflected electron. CONSTITUTION:The electron beam 1 is scanned by a deflecting coil 2 to illuminate the sample 3. Its reflected electron (e) is detected by reflected beam detectors 4a and 4b which are arranged symmetrically about the optical axis Z and their outputs are amplified by 5a and 5b and inputted to a tilt angle computing element 6. The angle distribution of the electron (e) depends upon the angle of incidence of the electron beam 1 on the surface of the sample 3. For the purpose, a specific calibration curve is found previously and then the tilt angle of the sample is detected by detecting the intensity of the reflected electron. Then, the output of the computing element 6 is integrated 7 to find the height coordinate. Here, the position coordinates of an adjacent point at fine position from an optional position on the sample 3 are found from measured values of the quantity of height variation and the tilt angle at the optional position and the coordinates of a next position are found similarly. This operation is repeated and the relation between the coordinate signal from a deflecting signal generator 9 and the height coordinate position from an integrating computing element 7 is displayed 8, so that surface roughness of the sample 3 is found quantitatively.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention makes it possible to quantitatively measure the unevenness formed on the sample surface by irradiating the sample with an electron beam, thereby making it possible to measure the so-called cross-sectional profile of the sample. This relates to a device that has been used.

[Prior art] For example, scanning Auger microprobe (SAM)
), in order to analyze the composition in the depth direction of a sample, the sample surface is intermittently or continuously irradiated with an ion beam to scrape the sample surface, while the sample is irradiated with an electron beam to measure the Auger electron intensity. Taking measurements.

In such a device, in order to quantitatively understand the depth of the unevenness (so-called crater) formed on the sample surface by ion beam irradiation, the sample surface is irradiated with the ion beam for a certain period of time, and then the sample is evacuated. Bring the sample chamber to atmospheric pressure, take out the sample, and check how much of the sample surface has been removed (
The so-called sputtering is measured using a stylus-type surface roughness meter, an interference microscope, or the like. Therefore, when analyzing a sample in which multiple elements are layered on a silicon wafer, for example, the surface of the sample is irradiated with an ion beam for a certain period of time, and the ion beam irradiation time and sputtering speed data that has been investigated in advance are used to analyze the sample. The thickness of the layers that make up the sample is analyzed by measuring the amount of sputtering on the surface.

[Problems to be Solved by the Invention] In such a conventional apparatus, since the sample is taken out from the sample chamber and measured, the sample is contaminated by the outside air, and it is difficult to irradiate the same analysis point on the sample with an ion beam. This becomes extremely difficult, and therefore it is impossible to know the amount of spatter from the sample surface during the analysis. In addition, when analyzing the above sample, irradiate the sample with an ion beam under certain conditions (for example, constant acceleration voltage), calculate the amount of sputtering from the ion beam irradiation time and sputtering speed, and convert the layer thickness. are doing. Therefore, since the amount of sputtering per unit time varies depending on each element constituting the sample, it is not possible to accurately determine the thickness of the layer when converting the amount of sputtering per unit time as a constant.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and provide an apparatus that can quantitatively measure the depth of irregularities on a sample surface during sample analysis.

[Means for solving the problem] The configuration of the present invention for solving the problem includes a means for irradiating an electron beam onto a sample, a means for scanning the electron beam on the sample, and a means for irradiating the electron beam. at least two detectors arranged symmetrically with respect to the optical axis of the electron beam for detecting reflected electrons scattered from the sample, and calculating an inclination angle of the sample surface based on the signal obtained from the valley detector. It is characterized by comprising a tilt angle calculator, an integral calculator placed after the tilt angle calculator, and means for quantitatively displaying or recording the unevenness of the sample surface based on the signal from the integral calculator. It is said that

[Example] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an electron beam emitted from an electron gun (not shown).The electron beam 1 is scanned by a deflection coil 2 and irradiates a sample 3.

Reflected electron e emitted from the sample 3 by irradiation with the electron beam 1
are two backscattered electron detectors 4a arranged symmetrically with respect to the optical axis 2 of the electron beam 1.

4b and amplified by amplifiers 5a and 5b,
It is input to a tilt angle calculator 6 that calculates the tilt angle of the sample.

The tilt angle calculator 6 calculates the sample tilt angle θX from the backscattered electron intensity IA detected by the anti-tJJ electron detector 4a and the backscattered electron intensity tr detected by the backscattered electron detector 4b. Reference numeral 7 denotes an integral calculator that integrates the signal from the tilt angle calculator 6 to obtain the height coordinate hx. 8 is a deflection signal (coordinate signal) X from the deflection signal generator 9 and a height coordinate signal h from the integral calculator 8.
This is a display device that records or displays the relationship of X.

In such an apparatus, the angular distribution of reflected electrons e from the sample 3 when the sample 3 is irradiated with the electron beam 1 depends on the incident angle of the electron beam with respect to the sample surface. In other words, as shown in FIG. 2(b), when the electron beam 1 is perpendicularly incident on the sample surface, the backscattered electron intensities IQ(θo) and Ir(θ0) received by the backscattered electron detectors 4a and 4b are are equal to IQ(θo)-1r<60). Here, as shown in FIG. 2(a), when the sample 3 is tilted to the left by θ-, the backscattered electron intensity IIZ(θ- ), Ir(θ-) becomes [(θ-)>Ir(θ-). Conversely, if sample 3 is tilted to the right by θ+,
As shown in FIG. 2(C), anti-fJJ electron detectors 4a, 4
The reflected electron intensity 112 (θ+) received by b.

Ir(θ+) is IQ(θ+)<Ir(θ+).

From the above relationship, from the backscattered electron intensity IQ and rr received by the electron detectors 4a and 4b, for example, the ratio I included/(I[+
If we put Ir)) as f (IQ, Ir), then f(I之, I
r) shows a change as shown in FIG. 3 with respect to the sample inclination angle θ, and in this case takes a value in the range of 0 to 1. Therefore, once the calibration curve of f (II2., rr) is determined from the sample inclination angle θ, the calibration curve of f (IQ, Ir) can be determined by detecting the backscattered electron intensity I, Ir. The inclination angle θ can be determined.

Here, if the inclination angle θ of the sample is determined, tan θX gives the first-order differential coefficient d h/d x at the coordinate X in the coordinate system of position X and height h.

Therefore, the unevenness of the sample surface can be quantitatively determined by h(X)=fo'''tanθxdx.

Here, if the sample 3 has irregularities as shown in Fig. 4, the change in height Δh at a minute distance ΔX from an arbitrary position (X+,'n+) is Δh1=Δxta.
nθ1 Therefore, XI+1=XI+ΔX h,+,=h,+Δxtanθ−, and the coordinates of the instantaneous point x1+1 can be obtained from the coordinate value x1 of an arbitrary position and the measured value of the inclination angle θ at xl. Again, the coordinates of the instantaneous point X1 and 2 are obtained from the total value of the inclination angle θ at point
By displaying the relationship between hx and the output hx of the integral calculator 7 on a display device, the unevenness of the sample surface can be determined quantitatively.

Figure 5 (a) shows the results of analyzing the elemental distribution in the depth direction of the silicon nitride layer on a silicon wafer by applying such a device to a scanning Auger microprobe.
) and (b). Fig. 5 (a) is an example in which the amount of sputtering at the ion beam irradiation time jt, iz...tn is displayed on the display device 8, and Fig. 5 (b) is displayed on the display device of the scanning Auger microprobe. FIG. 5 is a depth direction concentration distribution map obtained by ion beam irradiation time i+, iz...
. . . It is possible to know the state of change in the sputter amount in the depth direction and the relative concentration of each element constituting the sample. Therefore, for example, if you want to know the amount of sputtering on the sample surface at t2 during analysis, you can stop the ion beam irradiation to the sample surface and display the amount of sputtering on the display device 8, and you will know that, for example, 200 people have been sputtered. In this analysis example, it can be seen that the silicon nitride layer on the silicon wafer was laminated by 400 people.

In this way, it is possible to know the amount of spatter while referring to the sample analysis results during analysis without taking the sample out of the sample chamber, and it is also possible to analyze multilayer films by assuming a constant sputter value per unit time, unlike conventional equipment. This will improve the analysis results.

In the above embodiment, the amount of sputtering during ion beam irradiation time and the analysis results by the scanning Auger microprobe are displayed separately, but they may be displayed on a single display device.

Alternatively, four detectors for detecting reflected electrons from the sample may be arranged so that the tilt angles in both the X and Y directions can be measured simultaneously.

[Effects of the Invention] As detailed above, in the apparatus based on the present invention, when performing surface analysis of a sample, it is possible to quantify the depth of unevenness on the sample surface without taking the sample out of the sample chamber each time during sample analysis. Provided is a device that can perform measurements.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of an embodiment of the present invention, Figures 2 (a), (
b) and (c) are diagrams for explaining the backscattered electron intensity due to sample tilt, Figure 3 is a calibration curve of the backscattered electron intensity with respect to the sample tilt angle θ, and Figure 4 is for quantitatively measuring the unevenness of the sample. 5(a) and 5(b) are display examples when this device is used for SAM. 1: Electron beam, 2: Deflection coil, 3: Sample, 4a. 4b: backscattered electron detector, 5a, 5b: amplifier, 6: tilt angle calculator, 7: integral calculator, 8: display device, 9: deflection signal generator.

Claims (1)

[Claims] a means for irradiating an electron beam onto a sample; a means for scanning the electron beam on the sample; a detector, a tilt angle calculator that calculates the tilt angle of the sample surface based on the signals obtained from each detector, an integral calculator disposed after the tilt angle calculator, and the integral calculator A surface roughness measuring device using an electron beam, comprising means for quantitatively displaying or recording the unevenness of a sample surface based on signals from the surface of the sample.