JPH01140007A - Height measuring device - Google Patents

Abstract

PURPOSE:To measure a height without a dead angle generated on a whole surface of a material by means of a compact and simple structure by a method wherein two deflectors which deflect electron beams are used to measure a material from two optical axes. CONSTITUTION:First, an output signal only is used to drive a deflector 10 to search a scanning image to be measured, and when an object (mark) is found, a first and a second deflection circuits are driven. When an X-scanning image looks like Fig. (d), for example, an upper half of a y-direction screen is assumed to be 0 and a lower half is to be 1. When a flag is 0 (or 1), the scanning state is indicated by the solid line (or broken line) in Fig. (a). Therefore, the upper and lower halves of an object image differ horizontally as shown in Fig. (c). This difference decreases when a deflection angle theta2 of the deflector 10 is increased by adjusting the output signal of the second deflection circuit. When the difference is made to be zero as shown in Fig. (b), deflection angles theta1 and theta2 are calculated, and with the given equation, a distance between the deflector 10 and a material 2, that is the height 10 of the material surface is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a height measuring device used for measuring the height of a surface of a material to be exposed, such as an electron beam exposure device.

[Prior art] For example, when drawing a fine circuit pattern on a semiconductor wafer using an electron beam exposure device, if the height of the wafer surface deviates from the set height, the position and size of the exposed circuit may change. This results in a difference from the predetermined one, and the drawing accuracy is significantly reduced, especially when multiple exposure is performed on a semiconductor wafer. Therefore, accurately measuring the height of a semiconductor wafer is extremely important for performing highly accurate drawing.

FIG. 5 is a configuration diagram showing an example of a conventional height measuring device used for measuring the height of such a material surface. In the figure, 1 is a light source for irradiating the surface of material 2 from an oblique direction. The light from the light source 1 is incident on the lens 4 through an aperture formed in the member 3, and is imaged near the surface of the material 2.

5 is a lens disposed in the traveling direction of the light reflected on the surface of the material 2, so as to form a reflected image on the photoelectric detection surface of the image dissector tube 6. has been done.

The image dissector tube 6 generates a signal corresponding to the position of the image, and the height displacement of the surface of the material 2 is calculated based on the signal.

In such an apparatus, it is assumed that the material 2 changes by a height h from 2a to 2b as shown in FIG. Assuming that the distance between the virtual images P' and P'' of the aperture aP is the magnification of the L lenses 5, the incidence of M1 light is θ, and the reflection angle is θ, the deviation Δ of the aperture image on the detection surface is Δ−M·l cosθ! It is given by M·2 h cos θ.Here, since M and θ are known, the height displacement can be easily determined if Δ is determined.

The device configured in this way is non-contact and optical,
The surface height of the material at the irradiation point of the electron beam can be measured without affecting the electron beam in any way.

[Problems to be Solved by the Invention] However, the image dissector tube 6 used in such a device has a photoelectric conversion surface, an aperture plate, a second-order single-son multiplier tube, a collector electrode, an electrostatic lens, a deflection coil, and Since it consists of a power supply for each part, the structure is complex and large, making it difficult to install it in an exposure room or the like with a small space.

In addition, in such a device, since light is irradiated onto the material 2 from an oblique direction and is reflected in an oblique direction, the surface height of the material 2 stored in the cassette 7 as shown in FIG. When measuring, the edge of the material 2 becomes a blind spot of the cassette 7 and cannot be measured.

The present invention has been made in view of these points,
The object is to provide a height measuring device which is relatively small and simple in construction and is capable of measuring height over almost the entire surface of a material without creating a blind spot.

[Means for Solving the Problems] The present invention, which solves the above problems, includes a first deflector that deflects the electron beam to shift the optical axis of the electron beam irradiated onto the material, and an electron beam that passes through the first deflector. a second deflector that deflects the electron beam and irradiates the material; a scanning circuit that outputs a scanning voltage for scanning with a predetermined angular width to the second deflector; and a first deflector that has a different polarity according to a flag signal.
a first deflection circuit that outputs a deflection voltage of 1 to the first deflector, a second deflection circuit that outputs a second deflection voltage having a different polarity to the second deflector according to the flag signal;
The distance between the deflector and the second deflector is ji' t
, the deflection angle by the first deflection voltage is θ1, and the second deflection angle is set so that the scanned image of the material matches regardless of the switching of the flag signal.
The present invention is characterized in that it is comprised of a second deflector and calculation means for calculating the distance mlo to the material surface using the following equation, assuming that the tendency angle when adjusting the deflection voltage is θ2.

12o=11-tan θt/1an(θ2-
θ 1 ) [Function] In the height measuring device of the present invention, by measuring the position of the material from two optical axis directions using two deflectors that deflect an electron beam, the distance from the deflector to the material,
In other words, find the height of the material surface.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of the drive system shown in FIG. In the figure, 8 is an electron beam irradiated onto the material 2. 9 is a first deflector that deflects the electron beam 8 so as to shift the optical axis; 10;
is a second deflector for drawing that deflects the electron beam 8 that has passed through the first deflector 9 and irradiates the material. 1
1 is a proboscis lens, 12 is a backscattered electron detector, and 13 is a secondary electron detector. 14 is a scanning circuit that outputs a scanning voltage for linearly scanning a predetermined angular width θ0 at an arbitrary period to the second deflector 10, and its output signal is applied to one input terminal of the adder 15. There is. 16 is the angle of the electron beam ±θ1 according to the flag signal °11", 0".
A first deflection circuit outputs a first deflection voltage with a different polarity for deflection to the first deflector 9, 17 is a flag signal "1" 11 Q IT polarity for deflecting the electron beam at an angle of ±θ2 This is a second deflection circuit that outputs second deflection voltages having different values to the second deflector 10.

For example, in the case of the first deflection circuit 16, when the flag is 1, -θ
1 and outputs 101 when the flag is 0, and the second deflection circuit 1
In the case of 7, +θ2 when the flag is 1 and -θ when the flag is 0.
Outputs 2. Note that the output signal of the second deflection circuit 17 is applied to the other input terminal of the adder 15. Also,
The deflection type may be electrostatic deflection or 'rBIaII direction.

The operation of the device configured in this way is divided into two cases: (A) measuring the height while observing the scanned image of the material 2, and (B) measuring the height by detecting a mark set in advance. We will explain when to do this.

(A) Scanned image of material 2 I! When measuring the height while observing the object, first, the second deflector 10 is driven only by the output signal of the scanning circuit 14 to search for the object in the scanning image.

The scanning state at this time is as shown in FIG. 3(b).

d3 is the scanning width at this time. When an object as shown in FIG. 4(b) is found, the first deflection circuit 16 and the second deflection circuit 17 are also driven. Note that FIG. 3(a) shows the beam trajectory when only the first deflector 9 is driven. dl is the scanning width at this time. In the 11th case of the X-scanning image as shown in Fig. 4, if the upper half of the screen in the y direction is set to "O" and the lower half is set to "1", the flag is set to "
The scanning state when the flag is "0" is as shown by the solid line in Figure 3 (C), and the scanning state when the flag is "1" is as shown in Figure 3 (C).
) as shown by the dashed line. Therefore, the image of the object to be observed will be shifted vertically and horizontally, as shown in FIG. 4(a).

However, such an image shift can be reduced by adjusting the output signal of the second deflection circuit 17 and increasing the deflection angle θ2 of the second deflector 10, and finally the image shift as shown in FIG. 3(d) can be reduced. and can be matched as shown in FIG. 4(b). Deflection angle θ when the images are matched in this way! , θ2, the distance from the second deflector 10 to the material surface 2, that is, the height 10 of the material surface, is determined according to the following procedure.

In addition, the distance between the first deflector 9 and the second deflector 10! ! Set to 1. In Fig. 3(d), from ΔPAB, d2-2A'tjanθt''(1), then line segment AB
Since ΔPAQ is a right triangle with Q being the intersection point of In addition, θ2 is the line segment PA in the optical axis direction that was originally deflected by the optical axis shift deflector 9.
Since it is an inner coal that corrects C and PBD inward, the following formula holds true.

Otsu PAC - θ2 + Otsu OAB + Otsu PAB -2ZR - 180° ... (3) From this, Otsu 0AB = 2 Otsu R - θ2 - Otsu PAB Here, substituting the equation (2) of Otsu PAB, Otsu 0AB - 2
ZR-02 (OtsuR-θ1)-ZR+θ1-θ2
(4) Also, since ΔOAB is an isosceles triangle, dividing it by the line segment PO connecting points P and 0 on the original optical axis results in a right triangle.

Therefore, tanLOAB-line segment OQ/line segment AQ ・(5)
holds true. Moreover, the line segment OQ and Ifit segment AQ are expressed as follows.

Line segment 0Q-10...(6) Line segment AQ-62/2 ・<7> Then, by transforming equation (5) and substituting (6) and (7), line segment OQ-line segment AQ- tanZOAB From now on do = (d z /2) ・tanLOAB −
(8) Next, since ΔPAB is an isosceles triangle,
By vertically bisecting the line segment PQ, ΔPAQ becomes a right triangle. Therefore, tan ot APQ = line segment AQ/line segment PQ From this, tan θt − (d 2 /2>/Vt −
(9) Transforming equation (9), d 2 /2 = 1! +-tanθr −(10) Here, by substituting equations (4) and (10) using equation (8), we get 10=/1-tanθ1 −tan(,4R-) θ 1 − θ 2 )
・= (11) Transforming equation (11), 10=/s ・tanθ1 −tan (ZR−(θ2−θ1))=71−tan
θ+/1an(θ2−θri) (12) The height Ilo of the material surface can be determined by the equation (12).

In order to improve the measurement accuracy in this case, the value of θ0 may be decreased and the observation magnification may be increased from low to high magnification.

(B) When measuring the height by detecting a pre-provided mark First, as shown in FIG. Move the stage so that the mark is located directly below the axis. and,
The first deflection circuit 16 and the second deflection circuit 17 are also driven with the mark positioned directly below the optical axis. This results in
As in the case of (A>), the scanning state when the flag is 0'' is as shown by the solid line in Fig. 3 (C), and the scanning state when the flag is 1'' is as shown in Fig. 3 (C). ). Therefore, by adjusting the output signal of the second deflection circuit 17 and increasing the deflection angle θ2 of the second deflector 10, this appearance can be changed to the position of the upper mark. The deviations S* and S2 can be made smaller, and in terms of radius, they can be made to match as shown in FIG. <A) The distance from the second deflector 10 to the material surface 2, that is, the height 10 of the material surface is determined.

With this configuration, the height of the material surface can be measured by irradiating the material with an electron beam from a direction almost perpendicular to the material. There are no blind spots like this.

Furthermore, the height of even common materials can be measured when observed using a scanning electron microscope. In other words, if an electron beam can be irradiated and there is a mark or object to be observed, it is possible to measure the height of a fairly detailed area.

Furthermore, since the material position is fixed and the stage is not moved during height measurement, high-speed processing is possible.

[Effects of the Invention] As described above in detail, the present invention provides a height measuring device that is relatively small and has a simple configuration and can measure heights over almost the entire surface of a material without creating a blind spot. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of the drive system shown in FIG. 1, and FIGS. 3 and 4 are operation explanatory diagrams.
Figure 5 is a configuration diagram showing an example of a conventional height measuring device;
The figure is an explanatory diagram of the operation of FIG. 5, and FIG. 7 is a configuration diagram showing a specific example of materials stored in the cassette. 8... Electron beam 9... First deflector 10... Second deflector 14... Scanning circuit 15... Adder 1G...
・First deflection circuit 17...Second deflection circuit patent applicant Nippon Denshi Co., Ltd. Representative Patent attorney Ijima
Fuji Jigai 1 person (c) 2-Kaichi (d)

Claims (1)

[Claims] A first deflector that deflects the electron beam to shift the optical axis of the electron beam that is irradiated onto the material, and a second deflector that deflects the electron beam that has passed through the first deflector and irradiates it onto the material. a scanning circuit that outputs a scanning voltage for scanning with a predetermined angular width to a second deflector; and a first deflector that outputs a first deflection voltage having a different polarity to the first deflector in accordance with a flag signal. a second deflection circuit that outputs a second deflection voltage with a different polarity to a second deflector according to a flag signal; a distance between the first deflector and the second deflector is l_1; and a first deflection voltage. The deflection angle by θ_
1. Calculate the distance l_0 between the second deflector and the material surface using the following formula, assuming that the deflection angle when adjusting the second deflection voltage is θ_2 so that the scanned image of the material matches regardless of the switching of the flag signal. A height measuring device comprising: a calculation means for calculating the height; l_0=l_1・tanθ_1/tan(θ_2−θ_
1)