JPH042032A - Specimen stage control method for charged particle beam device - Google Patents

Abstract

PURPOSE:To make eucentric control automatically by determining the level of the specimen surface from phase difference between two types of sensing signals, and performing horizontal movement of the specimen automatically according to the leven determined, the inclination angle, and the distance of the part to be observed from the optical axis. CONSTITUTION:First a particular part of a specimen 2 is moved to the center of a stage (on an inclining axis A), and straight scan is made with an electron beam across a mark, wherein the inclination angle of the specimen is zero. The reflected electrons obtained are sensed by a sensor 6, and the sensing signal is stored in a waveform memory 9. The signal stored in this waveform memory 9 is stored in another memory 10. Then the specimen is inclined an angle theta. At this stage another straight scan is made with electron beam across the mark, and the signal sensed is stored in the memory 9. Then the signal stored in the waveform memory 9 is stored in another waveform memory 11. The phase difference between the signals stored in these memories 10, 11 is determined by a phase difference sensing unit 12. On the basis thereof the level (z) of the specimen surface by reference to the inclining axis is determined. The observe thereafter the position a distance (b) apart from the optical axis, automatic movement of the observing point on the specimen to the optical axis will take place when the specimen is inclined a specified angle (theta).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of controlling a sample stage in a scanning electron microscope or the like.

(Prior Art) In scanning electron microscopes and the like, a sample is not only moved horizontally in the X and Y directions, but also observed while being tilted. Therefore, the sample stage has a tilting mechanism and
An XY horizontal movement mechanism is provided above the tilting mechanism, and the sample is set on the horizontal movement mechanism.

(Problem to be Solved by the Invention) FIG. 2 is a diagram for explaining the relationship between the tilt of the sample and the observation position, where A is the tilt rotation axis of the sample stage,
S is the sample surface when the tilt angle is zero. Now, the optical axis O is at a sample surface position p which is a distance away from the rotation axis A, and when the part p is observed and the sample stage is then rotated by an angle θ, the sample surface S becomes S indicated by the dotted line in the figure. ', the observation position p is separated by ΔX from the optical axis O (the previous observation position) as shown by p', and the field of view is missed.

Therefore, after tilting the stage, it is necessary to control (eucentric control) using an XY horizontal movement mechanism so that p' is located directly below the optical axis.

This control method will be described below.

First, while viewing the observation screen of a scanning electron microscope, the amount of image movement ΔX when the tilt angle is θ is determined.

Here, the image movement amount ΔX has the following relationship, where zl is the height of the sample surface with respect to the tilt axis A.

ΔXI! z1 tanθ Therefore, 2, -Δx/lanθ The height of the sample surface can be found from ΔX and θ.

After that, when the sample is rotated by an arbitrary angle, the angle at that time and the already determined height of the sample surface are 2. From this, the amount of movement ΔX of the image is determined by a computer, and the horizontal movement mechanism is automatically controlled based on this ΔX, so that the field of view before tilting is moved directly below the optical axis.

However, the above-mentioned control method is limited to the height zl of the sample surface.
This step is not automated and must be performed by human observation of the image, which is very inconvenient.

The present invention has been made in view of the above-mentioned points, and its purpose is to realize a method for controlling a sample stage in a charged particle beam apparatus that can automatically perform eucentric control.

(Means for Solving the Problems) A method for controlling a sample stage in a charged particle beam apparatus based on the present invention is a method for controlling a stage that is provided with a mechanism for horizontally moving a sample in both X and Y directions on a tilting mechanism. Then, the characteristic part of the sample is moved onto the tilt axis by the tilt mechanism, and when the tilt angle of the sample by the tilt mechanism is zero, the characteristic part is scanned in a straight line, the detection signal based on this scanning is stored, and the tilt After setting the inclination angle of the sample by the mechanism to a constant angle, the characteristic part is scanned linearly by the charged particle beam, and the detection signal based on this scanning is stored, and the memorized 2
Determine the phase difference of the species detection signal, determine the height (21) of the sample surface from the tilt axis based on this phase difference, and then, when observing a position at an arbitrary distance (b) away from the optical axis, When tilted by a predetermined angle (θ), height z1, distance b1
It is characterized in that the observation point of the sample is automatically moved to the optical axis based on the angle θ.

(Function) Align the tilt axis of the sample stage with the optical axis, place the characteristic part such as a mark on the sample under the optical axis, and when the tilt angle is zero,
A characteristic portion is scanned linearly by a charged particle beam to obtain a detection signal, and then the same characteristic portion is scanned linearly by a charged particle beam with the sample tilted to obtain a detection signal;
The height of the sample surface is determined from the phase difference between the two types of detection signals, and then, when observing an arbitrary sample surface at an angle, the horizontal position of the sample is determined using the determined height, angle of inclination, and distance from the optical axis of the observation section. Move automatically.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to FIG. FIG. 1 shows an example of a scanning electron microscope implementing the sample stage control method according to the present invention, in which an electron beam EB is deflected by a deflector 1. Reference numeral 2 denotes a sample, which is placed on a sample stage 3, which has a tilting mechanism above a Z-direction vertical movement mechanism, and an XY horizontal movement mechanism above the tilting mechanism. A deflection signal is supplied to the deflector 1 from a deflector control unit 5 controlled by a computer 4, and based on the deflection signal, the electron beam EB is directed to the sample 2.
scanned above. For example, reflected electrons generated by irradiating the sample 2 with an electron beam are detected by the detector 6, and the detection signal is amplified by the amplifier 7, and the AD
After being converted into a digital signal by the converter 8, the first
is supplied to the waveform memory 9 and stored therein. A reference signal is supplied to the first waveform memory 9 from the deflector control unit 5 . The signals stored in the waveform memory 9 are supplied to either the second waveform memory 10 or the third waveform memory 11 and stored therein according to instructions from the computer 4. The signals stored in the second and third waveform memories 10.11 are
The signal is supplied to a phase difference detection unit 12, and the phase difference between both signals is determined.

A signal corresponding to this phase difference is supplied to the computer 4. Note that the computer 4 also controls the control unit 13 of the sample stage 3.

With the above-described configuration, first, a characteristic portion of the sample 2, such as a mark, is moved to the center of the stage (on the tilt axis A), and an electron beam is scanned linearly across the mark. At this time,
The tilt angle of the sample was set to zero. The reflected electrons obtained along with this scanning are detected by the detector 6, converted into digital signals by the AD converter 8, and supplied to the first waveform memory 9, where they are stored according to the scanning position of the electron beam. Ru. This linear electron beam scanning is performed many times to increase the S/N ratio of the detection signal, and the detection signal corresponding to each scanning position is integrated in the first waveform memory 9. After being integrated, the signal stored in the first waveform memory 9 is transferred to and stored in the second waveform memory 10.

Next, the stage control unit 13 is controlled by a command from the computer 4, and the tilting mechanism of the stage 3 is driven to tilt the sample at an angle θ. At this stage, the electron beam is linearly scanned across the mark again, and the signals detected during the scanning are supplied to the first waveform memory 9 via the AD converter 8 and stored therein. In this first waveform memory 9, the detection signals are integrated, and after a predetermined number of image-line scans of the electron beam are completed, the signals stored in the first waveform memory 9 are as follows.
It is transferred to and stored in the third waveform memory 12. next,
The phase difference between the signals stored in the second and third waveform memories 10.11 described above is determined by the phase difference detection unit 12. Here, X is the scanning position of the electron beam, and the second
The waveform data in the third waveform memory 11 is f(x), and the waveform data in the third waveform memory 11 is g(x). The autocorrelation R(i) of these two types of waveforms is determined by the phase difference detection unit 12, and R(i) can be expressed as follows.

R(f) −Σf (j) ・g (i+j)
... (1) The phase difference detection unit 12 performs the calculation shown in the above equation (1),
That is, the addresses of f (x) and g (x) are shifted by i, multiplied together, and the sum is calculated. And m
Letting be the maximum value of memory address, i--(m-n)..., 0. ..., (m-n
) is the value of i (ΔX
) is required. That is, the value of i becomes the phase difference (image shift amount in the X direction) of the detection signal waveform when the tilt angle of the sample surface is 00 and when the tilt angle is θ.

Here, the phase difference ΔX can be expressed as follows from FIG.

Δxwb+z+ tanθ−b/cosθ...
(2) In the above equation, the unknown variables are zl and b, but when the phase difference is calculated, since the mark is placed at the center of the stage (on the tilt axis), it becomes b-o. Therefore, Equation (2) becomes Δx −z , tanθ, and zl−Δx/lanθ is derived, and the height zl of the sample surface can be determined by calculation.

In the above step, the height zl of the sample surface is automatically determined. After that, when observing a sample part at an arbitrary part (a distance from the tilt axis) by tilting it, the height zl of the sample surface is automatically determined. The amount of movement of the observation position in the X direction is determined by the above equation (2), and the sample is moved in the X direction by the amount of movement. As a result, the observation part is located directly below the optical axis, eucentric control can be performed, and even if the sample is tilted, the image can be prevented from escaping. Further, the height deviation amount Δ2 in the Z direction is determined by the following equation.

Δz−b” tan θ+Zr z+/cos θ The stage is driven in the Z direction according to the value of Δ2 thus obtained, and the sample before and after tilting can be observed at the same height.

Although the present invention has been described in detail above, the present invention is not limited to this embodiment. For example, although reflected electrons are detected, secondary electrons may also be detected. Furthermore, although the scanning electron microscope has been described as an example, the present invention can also be applied to ion beam devices and the like. Furthermore, although the mark is scanned when determining the height of the sample surface, feature points on the sample other than the marks may be used.

(Effects of the Invention) As described above in detail, in the present invention, the tilt axis of the sample stage and the optical axis are aligned, the characteristic parts such as marks on the sample are placed under the optical axis, and the tilt angle is adjusted to zero. At this time, a detection signal is obtained by scanning a characteristic part in a straight line with a charged particle beam. Next, the sample is tilted and the same characteristic part is scanned in a straight line with a charged particle beam to obtain a detection signal. The height of the sample surface is determined from the phase difference of the detection signal, and then when performing tilted observation of any sample surface, the horizontal movement of the sample is automatically performed based on the determined height, tilt angle, and distance from the optical axis of the observation section. Therefore, all eucentric control of the sample stage can be performed automatically.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a scanning electron microscope for implementing the stage control method based on the present invention, and FIG. 2 is a diagram for explaining the relationship between the inclination of the sample and the observation position. 1...Deflector 2...Sample 3...Sample stage 4...Computer 5...Deflector control unit 6...Detector 7...Amplifier 8...A
D converter 9.10.11... Waveform memory 12... Phase difference detection unit 13... Stage control unit

Claims (1)

[Claims] A method for controlling a sample stage in a charged particle beam apparatus equipped with a mechanism for horizontally moving a sample in both X and Y directions on a tilting mechanism, the method comprising: moving a characteristic part of the sample onto a tilt axis by the tilting mechanism; When the tilt angle of the sample is zero, the characteristic part is scanned in a straight line, the detection signal based on this scanning is stored, and after the tilt angle of the sample by the tilt mechanism is set to a constant angle, the characteristic part is charged. The particle beam scans in a straight line, the detection signal based on this scanning is stored, the phase difference between the two stored detection signals is determined, and the height (z_1) of the sample surface from the tilt axis is determined based on this phase difference. ), and then when observing a position at an arbitrary distance (b) from the optical axis and tilting the sample at a predetermined angle (θ), the sample is automatically adjusted based on the height z_1, distance b, and angle θ. A method of controlling a sample stage in a charged particle beam device in which the observation point of the sample is moved along the optical axis.