JPS5895204A - Detection for sample position - Google Patents

Abstract

PURPOSE:To detect a sample position with a high precision in a high speed independently of the shape of a mark, by scanning the mark on the surface of the sample circularly with an electron beam and detecting the sample position on a basis of the value of intervals of reflected electrons obtained by measurement. CONSTITUTION:A radiated electron beam of an electrooptical system 10 is deflected to a shape like a circle by a deflecting means 11 and is irradiated to a mark 1, which is formed with plural lines intersecting each other, on the surface of a smaple to scan the mark 1 circularly. The reflected beam generated by scanning is detected by a detector 15 and is amplified and becomes a detection signal 16. Deflecting signals 13 and 14 are inputted to differentiating circuits 21 and 22, and intervals of generation of the signal 16 is measured by discriminating signals 23 and 24. The deviation of center coordinates of the mark 1 is obtained on a basis of this measured value, and a prescribed value is added to or subtrated from center coordinates of the beam, and the actual center coordinates of the mark 1 and the sample position are calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sample position detection method for detecting a sample position by scanning a position detection mark attached to a sample with an electron beam or the like.

Conventionally, there are the following detection methods of this type.

That is, as shown in FIG. 1, a mark 1 in the shape of a "mouth" is formed on the surface of a sample, and this mark 1 is sequentially scanned by a horizontal electron beam 2 and a vertical electron beam 3. By the detection signals 4 and 5 of the reflected beam obtained when the electron beam passes through the end of the mark 1,
There is a method in which center coordinate positions 6 and 7 of mark 1 are calculated and these center coordinate positions are set as the sample position.

However, in this detection method, if the mouth-shaped mark 1 is made smaller in order to improve the accuracy of the detection position coordinates, many preliminary scanning beams 8 are required to detect the end of this mark 1. The disadvantage is that the detection time is long. Furthermore, since the scanning control waveform 9 for sequentially moving the electron beams 2 and 3 becomes a sawtooth wave as shown in FIG. 2, high-speed scanning becomes difficult, and there are pauses between each scanning period. This method has the disadvantage that the mark position cannot be detected at high speed because the period t is required.

An object of the present invention is to provide a sample position detection method that allows the sample position to be detected with high precision and high speed.

In the present invention, a mark formed on the surface of a sample by a plurality of intersecting straight lines is scanned in a circular manner by an electron beam, and the time interval of backscattered electrons generated when the electron beam crosses each straight line of the mark is measured. The center position of the mark is calculated from the measured value, and the sample position is detected based on this calculated value.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.

FIG. 3 is a block diagram showing one embodiment of the present invention. In the figure, an electron beam emitted from an electron optical system 10 is circularly deflected by a deflection means 11 in two directions, X and Y, such as a deflection coil and an electrostatic polarizing plate. This circularly deflected electron beam is irradiated onto a mark 1 formed by a plurality of straight lines that intersect with each other on the surface of the sample, and scans the mark 1 in a circular manner. In this case, deflection circuit 1
As the deflection signals given to the deflection means 11 from the X-direction deflection signal 13, sinusoidal waveform signals such as Acos t and As+inωt are used as the X-direction deflection signal 14.

When the mark 1 is scanned by an electron beam, a reflected beam is generated at the timing when the electron beam crosses each straight line of the mark 1. This reflected beam is detected by a detector 15 and then amplified to become a detection signal 16.

For example, when a mark 1 formed by two orthogonal straight lines is scanned by a circular electron beam with the center coordinates (ΔX, Δy) as shown in FIG. A detection signal 16 as shown in FIG. 4(d) is generated at a position 17°18.19.20 across the straight line.

Therefore, the deflection signals 13 and 14 are input to differentiating circuits 21 and 22, respectively, and the differentiating circuit 21 outputs an identification signal 24 indicating that the electron beam is in the fourth and third quadrants.
(FIG. 4(e)), and the differentiation circuit 22 generates an identification signal 23 (FIG. 4(f)) indicating that the electron beam is in the third and second quadrants. . Based on these identification signals 23 and 24, the generation interval tI + of the detection signal 16 of the reflected beam is
Measure '2 +t3+'4.

Then, as shown in FIG. 5, the deflection α between the intersection 20 and the center coordinate ΔX of the y-axis of the electron beam, and the deflection B between the intersection 17 and the center coordinate Δy of the y-axis of the electron beam are expressed by the following equations, respectively. It will look like the one shown below.

Therefore, the center coordinates ΔX and Δy of the electron beam can be determined by the following equation, where γ is the radius of the electron beam.

ΔX=γsinα That is, the deviation of the center coordinates of the electron beam with respect to the center coordinates (x, y) of the mark 1 can be determined. Therefore, the center coordinates of the electron beam (ΔX,
By adding or subtracting a predetermined value from Δy), the actual center coordinates (x, y) of the mark 1 can be determined.

Incidentally, the calculations of equations (3) and (4) above can be obtained by an arithmetic circuit as shown in FIG.

That is, the first adder 25 calculates the time interval t, ~t
4 (t, -1-t2+'t, +t, ) is calculated, and the value of this sum is inputted to the dividers 28 and 29 as a divisor value. On the other hand, the second adder 26 calculates r(tz+t
s) Find (tl+t4)J and input this calculated value to the divider 28 as the dividend value. Also, the third adder 27 inputs r<t, -1-t2)-(t3+t4
)" and inputs this calculated value to the divider 29 as the dividend value. Then, a calculation is performed in the divider 28 and the calculated value is input to the sine function generator 30. Thereby, a calculated value indicating the center coordinate Δ-y of the electron beam can be obtained from the sine function generator 30.

On the other hand, the divider 29 performs a calculation and the calculated value is input to the sine function generator 31. Thereby, a calculated value indicating the center coordinate ΔX of the electron beam can be obtained from the sine function generator 30.

In this way, in the present invention, marks formed on the surface of a sample are scanned in a circular manner by an electron bean, and the sample position is detected based on the measured value of the generation interval of reflected electrons obtained by this scanning. , the sample position can be detected with high accuracy regardless of the size of the mark shape. Furthermore, since a sine wave is used to control the scanning of the electron beam, high-speed scanning is possible, and the sample position can be detected at high speed.

Further, since the scanning is circular, there is no need for preliminary scanning as in the conventional method, and there is an effect that high-speed position detection can be further promoted.

[Brief explanation of the drawing]

Figure 1 shows an example of a conventional sample position detection method;
The figure is a waveform diagram for scanning control of the electron beam, Figure 3 is a block diagram showing an embodiment of the present invention, Figure 4 is a time chart for explaining its operation, and Figure 5 is the center position of the mark. FIG. 6, which is an explanatory diagram of the method for determining , is a diagram showing an example of the arithmetic circuit. DESCRIPTION OF SYMBOLS 1... Mark, 10... Electron optical system, 11... Polarization means, 12... Deflection circuit, 15... Detector, 21
．． 22...Minute 10th 20th

Claims (1)

[Claims] 1. Cross. - a scanning means for circularly scanning marks for sample position detection formed on the surface of the sample by a plurality of straight lines with an electron beam; a detection means for detecting reflected electrons generated when the electron beam crosses each straight line; A method for detecting a sample position, comprising: a measuring means for measuring a detection signal interval of reflected electrons; and a calculating means for calculating a mark center position and a sample position based on the measurement output of the measuring means.