JPS62122043A - Measuring device for rotational angle of sample - Google Patents

Abstract

PURPOSE:To make it possible to measure a rotational angle of a wafer when a sample stage is mounted, on the basis of one wafer mark or a pattern configuration without using stage movement, by measuring the line width or the pitch interval of the water mark or the like, through rotating the scanning direction of a beam by a known amount. CONSTITUTION:The contact point 'i' of a switching circuit 16 is selected by a control unit 19, and constant (a) and (b) of constant circuits 14, 15 are respectively set by the control unit 19. For instance, a deflection signal X from a deflection signal generator 10 is multiplied by the constant (a) at a multiplier 13, and then the result is added with the constant (b) by an adder 12. The obtained deflection signal aX+b deflects a charged beam in Y direction through a deflection amplifier 8. Therefore, a charged beam 3 scans on a wafer obliquely at an angle of tan theta=a with respect to a stage coordinate system. An obtained video signal is processed by a signal processing circuit 17 to detect coordinates, and a pattern width (or a pitch distance) projected in X direction of the deflection signal is measured by a dimension calculating circuit 18. The signal processing circuit 17 performs slice level processing, peak value detection processing, etc. based on the waveform of the video signal to obtain coordinate data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a scanning charged beam device, and more particularly to a measuring method and device suitable for detecting a rotation angle that occurs when a wafer sample or the like is loaded onto a moving stage.

[Background of the invention]

In recent years, with the miniaturization of semiconductors, devices using charged particle beams such as electron beams have begun to be used for processing and inspecting wafers. These devices require that the position on the wafer can be specified accurately. However, when loading the wafer onto the sample stage, the wafer is mounted rotated with respect to the moving direction of the stage due to mechanical errors or the like.

FIG. 1 is a plan view schematically showing the relationship between a wafer and a sample stage. Coordinate axes of wafer 1 (XW, Yw)
is the coordinate axis (Xs, Y
An angular error β is generated between the angle and the angle s). Conventionally, the method for measuring the rotation angle β of a wafer is to use two wafer marks M for alignment.

It is well known to detect the position of N by beam scanning and associate it with the stage coordinates [for example.

Proceedings of the Symposium on Electron and Ion Beam Science and Technology (Proc, Symp.
, on 9th International Con
ferenceon Electron and Io
n Rears 5science and Techna
112-125 (1980)]. However, in this method, since the distance MN between the wafer marks is large, the second wafer mark N must be searched over a considerably wide area after the stage has been moved. Normally, this search range is larger than the beam scanning range S, so first widen the beam scanning range (i.e., use low magnification) to roughly discover its presence, and then reduce the scanning range (i.e., use high magnification). It was necessary to accurately detect the position coordinates.

Furthermore, in order to reduce the angular error, some methods take steps such as adjusting the wafer 1 with a pre-alignment holder (omitted in FIG. 1) outside the apparatus and loading the wafer 1 together with the holder onto the sample stage 2.

[Purpose of the invention]

An object of the present invention is to provide a method and apparatus for measuring a wafer rotation angle when a sample stage is loaded from a single wafer mark or pattern figure without using stage movement.

[Summary of the invention]

To achieve the above purpose, the present invention rotates the beam scanning direction by a known amount and measures the line width or pitch interval of the wafer marks, etc.

The wafer rotation angle with respect to the sample stage is calculated from this measured dimension and the beam scanning rotation angle. FIG. 2 is a scanned image of the wafer mark M, and the portion included in the beam scanning range S is enlarged.

Here, the description will be made assuming that the beam scanning direction and the stage movement direction match (this assumption is generally satisfied in this type of apparatus). As shown in Fig. 3, if the beam scanning direction is rotated by 10 degrees with respect to the stage coordinate axis
'Have an intersection at point z.

From the change in the intensity of the video signal at this time, the O
A dimension Q+ corresponding to the mark line width PIP2 in the A force direction is measured. Similarly, when the beam scanning direction is rotated 10 times and the OB is scanned, the mark line width page Q=Q- can be measured. From this result, the angle α (=90″+β) between the stage coordinate axis Xs and the wafer coordinate axis Yw can be obtained by the following equation.

Here, since tanθ is an immediately known quantity, the wafer rotation angle β
can be determined.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a block diagram of a scanning charged beam device having the present rotation angle measuring device. The charged beam 3 is a lens system (
(not shown) and scanned over the wafer 1 by deflectors 4 and 5 to process and inspect the wafer. Since the scanning range of the charged beam 3 is usually small, the wafer 1 is moved by the sample stage 2 to process and inspect the entire surface of the wafer. However, when loading the wafer 1 onto the sample stage 2, an angular error occurs as described above, causing the sample stage coordinates (Xs*Ys) and the wafer coordinates (X
w, Yw) are shifted. For this reason, it is not possible to position the specified position on the wafer directly under the charged beam by moving the sample stage. For example, if the wafer size is 100IIn and the angular error is 10mrad, the diameter at both ends of the wafer is 100μ.
A displacement of as much as m occurs. Therefore, it is essential to measure the rotation angle of the wafer and correct the stage movement.

The charged beam 3 receives a deflection signal X from a deflection signal generator 10,
The wafer is two-dimensionally scanned by Y via deflection amplifiers 7 and 8. In this case, the contact port of the switching circuit 16 is selected by the control unit 19. Video signals such as secondary electrons generated from the wafer surface by the scanning of the charged beam 3 are detected by the detector 6 and supplied to the display device 11 via the signal amplifier 9. The display device 11 includes a deflection signal generator 1
o, and a two-dimensional image of the wafer surface can be obtained here. The above is the basic configuration of scanned image display. The rotation angle correction method of the present invention is carried out as follows by finding a wafer mark or an arbitrary pattern figure parallel to the coordinate axis of the wafer on the display device 11.

First, the control section 19 selects contact A of the switching circuit 16. Constants a and b of constant circuits 14 and 15 are set by the control unit 19, respectively. For example, the deflection signal X from the deflection signal generator 10 is multiplied by the constant a in the multiplier 13, and then added by the constant a in the adder 12. The deflection signal aX+b thus obtained deflects the charged beam in the Y direction via the deflection amplifier 8. Therefore, the charged beam 3 is scanned obliquely over the wafer at an angle tanθ=a with respect to the stage coordinate system. The resulting video signal is processed by the signal processing circuit 17 to detect coordinates, and the dimension calculation circuit 18 measures the pattern width (or pitch distance) projected in the direction of the deflection signal X. The signal processing circuit 17 performs slice level processing, peak value detection processing, etc. on the video signal waveform to obtain coordinate data. Further, the dimension calculation circuit converts it into Q+ using the scanning width, that is, the magnification. Similarly, by setting the constant given to the constant circuit 14 as -a, the same pattern width (or pitch distance) Q- obtained using the deflection signal -a X + b is measured. can be calculated from equation (1) above. From this, the wafer rotation angle β=α−90@ is determined, so the stage coordinates (Xs
, Ys) becomes. If the stage is moved by the X motor drive circuit 20 and the Y motor drive circuit 21 via the stage control circuit 22 using the above relationship, the designated position for wafer rotation can be accurately moved directly below the charged beam.

In addition, as a dimension inspection device, pattern dimension Q OMITI
If we use the measured dimension Q3 in the beam deflection direction and the angle α according to equation (2) as shown in Fig. 6, then Q = Q 5 cos α ・・・・・・・・・
...(4), an accurate value corrected for errors due to wafer rotation is obtained.

In the embodiment shown in FIG. 5, the beam rotation has been explained based on the deflection signal X for the sake of simplicity.
It is also possible to supply a deflection signal Y to.

FIG. 7 shows another embodiment, in which the deflection signal synthesizer 23
sine/cosine potentiometer 33゜34 and adder 31
．． 32 to synthesize rotational deflection signals. Furthermore, in order to improve the accuracy of the rotational deflection signal, it is also possible to read sine and cosine function values from a read-only memory and synthesize them.

〔Effect of the invention〕

According to the present invention, since the rotation angle of the wafer can be measured from one pattern figure, the measurement speed can be increased compared to the conventional method using stage movement. In addition, pre-alignment of the rotation angle related to the search range of the second mark is no longer required, and the so-called cassette-toe-cassette method is used, in which one wafer is mechanically extracted from a cassette that transports multiple wafers and attached to and detached from the sample stage. It is suitable for measuring the wafer rotation angle. Furthermore, the rotation angle measurement according to the present invention can in principle be applied to an apparatus having a stage without a distance measurement function.

[Brief explanation of drawings]

Fig. 1 is a plan view showing the rotation angle of the wafer loaded on the sample stage, Fig. 2 is a scanned image of the wafer mark by beam scanning, and Fig. 3 is for explaining the principle of the wafer rotation angle 8111 method of the present invention. 4 is a schematic diagram of a video signal waveform from a mark figure, FIG. 5 is a block diagram showing an embodiment of the present invention, and FIG. 6 is an explanatory diagram of pattern dimensions on a rotated wafer. FIG. 7 is a partial configuration diagram showing another embodiment of the present invention. ■... Wafer, 2... Sample stage, 3... Charged beam, 4.5... Deflector, 6... Signal detector,
7, 8... Deflection amplifier, 9... Signal amplifier, 10.
...Deflection signal generator, 11...Display device, 12...
Adder, 13... Multiplier, 14.15... Constant circuit, 17... Signal processing circuit, 18... Dimension calculation circuit,
19...Control unit, 20°21...Motor drive circuit,
22... Stage control circuit, 23... Deflection signal synthesis unit, 31.32... Adder.

Claims (1)

[Scope of Claims] 1. A scanning device that deflects a charged beam two-dimensionally, a signal detection device that detects a signal generated from the sample by the scanning, and a signal processing device that extracts the position coordinates of the sample from the detection signal. In the scanning charged beam device, a reference is obtained from a deflection signal rotating means for rotating the scanning direction of the charged beam, and a dimension measurement value of the same reference figure obtained by rotating the scanning direction in at least two directions and a rotation angle of the charged beam. A measuring device for measuring a rotation angle of a sample, characterized in that it is provided with means for calculating an angle of a figure. 2. Orthogonal deflection signals (X, Y) as deflection signal rotation means
to synthesize an inclined linear signal (for example, aX+b, where a and b are constant values) from one of the deflection signals (for example, the X deflection signal) and use it as another deflection signal (for example, the Y deflection signal). 2. The sample rotation angle measuring device according to claim 1, further comprising a deflection signal synthesis section. 3. As a deflection signal rotation means, from the orthogonal deflection signal to the sine,
2. The sample rotation angle measuring device according to claim 1, further comprising a deflection signal synthesis section that synthesizes rotational deflection signals using a cosine function.