JPH07107891B2 - Electron beam writer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam writing apparatus, and more particularly to an electron beam writing apparatus suitable for increasing the accuracy of mark detection.

[Background of the Invention]

When drawing a certain area with an electron beam, a method is generally used in which the area is subdivided into virtual small areas and the drawing of the entire area is completed while sequentially drawing the small areas.

The condition required for drawing a small area is that high-speed drawing is possible from the viewpoint of improving throughput. From this point, electrostatic deflection capable of high-speed deflection control is used for drawing a small area. This deflection is commonly called the sub-deflection.

On the other hand, the movement of the electron beam between the small regions is required to have less deflection distortion than the high speed operation. From this point, in the case of large deflection, electromagnetic deflection having less distortion than electrostatic deflection is used. This is commonly called main deflection.

The electron beam deflection data is digitalized for high reliability. Therefore, a DAC (Digital-Analog Converter) is required to control the deflection with this data. As this DAC, a high-speed DAC with a small number of bits is used for drawing a small area (electrostatic deflection), and a high-resolution DAC is used for moving an electron beam between small areas (for electromagnetic deflection).

The address unit is the minimum unit of beam deflection at the time of drawing or mark detection, and the deflection field corresponds to the maximum range of the high resolution DAC.

In recent years, the electron beam drawing apparatus has reached the limit in the dynamic range of a general high resolution DAC due to the demand for large angle deflection and miniaturization for high speed and high accuracy. In particular, it is no longer possible to deal with measuring the length of a drawing pattern and improving the accuracy of mark detection used for beam calibration. That is, the address unit is conventionally determined from the drawing accuracy, and the same value is used for drawing and mark detection. Therefore, in the mark detection, the detection uncertainties corresponding to the same address units as at the time of drawing remain.

Originally, the device calibration should be more accurate than the address unit of drawing, and the deflection control at the time of mark detection needs to be made finer.

[Object of the Invention]

An object of the present invention is to provide an electron beam drawing apparatus capable of deflection control that achieves finer mark detection and higher accuracy.

[Outline of Invention]

A feature of the present invention is that the sub-deflection address unit can be set to a plurality of different values.

Example of Invention

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

FIG. 1 shows a variable shaped beam type electron beam drawing apparatus. The variable shaped beam method is a method in which the conjugate cross section of the first rectangular aperture 2 and the second rectangular aperture 4 of the beam emitted from the electron source 1 is controlled by the shaped deflector 3 to obtain an arbitrary rectangular shaped beam. The shaped beam is reduced by the reduction lens 5 and imaged on the surface of the sample 9 by the objective lens 6. Further, the main deflector 8 and the sub-deflector 7 deflect the beam to form an exposure pattern at a desired sample surface position.

FIG. 2 shows a block for deflector control. Calculator 10
The deflection data is transferred to the main deflection DAC circuit 11 and the sub deflection DAC circuit 12. Each DAC circuit outputs deflection data as an analog output, and the main and sub deflector amplifier circuits 14 and 13 drive the main and sub deflectors 8 and 7, respectively. The sub-deflection amplifier circuit 13 makes the deflection output variable by the sensitivity switching circuit 15 as necessary. That is, in the example, the sub-deflection address unit is set to a desired value by the sensitivity switching switch 15 of the sub-deflection amplifier circuit 13.

The principle of improving the mark detection accuracy by halving the address unit at the time of mark detection will be shown using Figs.

FIG. 3 shows the structure of mark detection. The sub-deflector 7 scans the mark 16 with an electron beam, and the detector 17 detects backscattered electrons and secondary electrons at that time. The comparator 18 compares the detection signal with a constant level. The mark position is obtained from the position where the signal peak crosses the level in FIG. However, the fifth
As shown in the figure (enlarged view of the edge detection section), since the deflection is controlled in address units, the point A where the signal crosses the level is
It has uncertainty from X to X + 1/2. However, in the conventional method, the uncertainty is from X to X + 1, and the accuracy is doubled by this method.

In the present embodiment, the address unit switching is performed by the deflection amplifier sensitivity switching, but as another method, the amplifier circuit may have multiple stages, and the number of stages may be changed or the amplifier circuit itself may be switched as necessary. But it is possible. Sub-deflection
Since the DAC has a lower bit than the main deflection DAC, it is easy to use a DAC with a higher bit, and a method of using the lower bit only when fine deflector control is necessary at the time of mark detection etc. can be considered. . In this case, it is not necessary to switch the sensitivity of the deflection amplifier.

Also, the setting value in the address unit can be selected as an arbitrary value depending on the accuracy requirement if the sensitivity of the deflection amplifier circuit is variable.

〔The invention's effect〕

According to the present invention, the deflection dynamic range is expanded with a DAC having a relatively low bit, regardless of the high resolution of the deflection DAC. In particular, it is possible to reduce the deflection quantization error at the time of detecting the mark and improve the apparatus calibration and the pattern length measurement accuracy.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of an electron beam drawing apparatus, FIG. 2 is a block diagram of a deflection control circuit of the present invention, FIG. 3 is a mark detection configuration diagram, and FIGS. is there. Common to all figures, 1 ... Electron source, 2 ... First rectangular aperture, 3 ... Molding deflector, 4 ... Second rectangular aperture, 5 ... Reduction lens, 6 ... Objective lens, 7 ... … Sub-deflector, 8 …… Main deflector, 9 …… Sample, 10 …… Calculator, 11 …… Sub-deflection DAC circuit, 12 …… Main deflection DAC circuit, 13 …… Sub-deflection amplifier circuit, 1
4 …… Main deflection amplifier circuit, 15 …… Sensitivity switching circuit, 16 ……
Mark, 17 ... Detector, 18 ... Comparator.

Claims (2)

[Claims] 1. A means for generating an electron beam, a deflector for deflecting the electron beam to a desired position on a sample surface, a deflection DAC circuit for converting deflection data into an analog output, and an amplifier for amplifying the analog output to obtain the analog output. In an electron beam drawing apparatus including a deflection amplifier circuit for driving a deflector, a selection unit that selects a deflection address unit, and an amplification factor changing unit that changes the amplification factor of the deflection amplifier circuit based on the output of the selection unit. An electron beam drawing apparatus having: 2. The electron beam drawing apparatus according to claim 1, wherein the deflector has a main deflector and a sub-deflector.