JPH0697060A - Electron beam lithography equipment - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to improve the S / N of a mark waveform without lowering the detection speed, and to improve the accuracy of mark presence detection and the accuracy of mark position detection. A mark waveform adder circuit centering on an adder 103 is provided in a stage preceding a conventional edge detection circuit 107, and edge detection processing is performed for each addition of a cumulative addition waveform and addition is made to a mark presence detection determination criterion by edge detection. By adding a saturation condition, the S / N ratio of the mark waveform is improved, and the mark presence detection success rate is improved.
Further, the position detection reproducibility is improved by detecting the edge position for each addition in the cumulative addition waveform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can improve the detection accuracy and accuracy of the presence detection and the position detection of the alignment mark having a lowered S / N due to the semiconductor process or the environment of the device without lowering the processing speed. The present invention relates to a possible electron beam drawing apparatus.

[0002]

2. Description of the Related Art Conventionally, the presence of a mark and the position of a mark are detected by detecting the edge of the mark waveform. However, there are problems such as a decrease in the success rate of presence detection and a decrease in the accuracy of position detection.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the S / N ratio of a mark waveform without lowering the detection speed, and improve the success rate of mark presence detection and the accuracy of mark position detection.

[0004]

In order to achieve this object, in the present invention, S / S is calculated by cumulatively adding detected waveforms.
By improving N and performing edge detection for each addition, the success rate of edge detection is improved and the position detection accuracy is also improved. Further, since the edge detection is performed for each addition, the detection is completed at the end of scanning,
It does not slow down the conventional detection speed.

[0005]

That is, in detecting the presence of the mark, the electron beam is scanned from the position where there is no alignment mark, but the noise component of the base is reduced by adding the signal corresponding to the base of this mark waveform. The signal components of the mark waveform generated when scanning the alignment mark at the same time are added to enhance the signal component, thereby improving the S / N. In addition to the conventional mark presence detection condition that a specified number of waveforms have a specified number of edges, there are more than a specified number of waveforms that have a specified number of edges and saturation occurs in the added waveform (overflow occurs. By setting the condition (1) as the mark existence condition, it is possible to improve the existence detection success rate even for a mark waveform having a low S / N low contrast.

In the mark position detection, the S / N of the signal is improved by adding the mark waveforms, and the detection accuracy,
Especially, the detection and reproduction accuracy is improved. Also, the added waveform is always 1
By performing edge detection processing as / 2, increase in waveform base due to cumulative addition can be avoided, and position detection can be performed without changing edge detection conditions as compared with the conventional method.

[0007]

EXAMPLE An example of the present invention will be described with reference to FIG. FIG. 1 is a functional block diagram for realizing the present invention, and the entire configuration of the electron beam drawing apparatus is shown in FIG. In FIG. 2, the electron beam emitted from the electron gun 202 at the top of the mirror 201 is controlled by the electron optical system 203 and the deflector 204, and is irradiated on the sample 205 on the XY stage 206 controlled by the stage control system 211. It Electron optical system 203 and deflector 20
4 is controlled by a lens power source 208 and a deflection control system 209, respectively. The backscattered electrons from the sample 205 are detected by the semiconductor detector 207 and after A / D conversion in the signal processing unit 210 which is the relevant part of the present invention, the result of performing arithmetic processing such as edge detection depending on the processing mode. Are taken into the control computer 213. The control system 212 mainly performs drawing control.

Reflected electrons from the sample detected by the semiconductor detector 116 shown in FIG. 1 are appropriately amplified by the amplifier 115 and then converted into digital signals by the A / D converter 114. Here, it is assumed that it is converted into a 12-bit digital signal. The digitized backscattered electron detection signal is latched by the flip-flop 101 synchronized with sampling. The inverted and non-inverted outputs of the flip-flop 101 are connected to the two inputs of the multiplexer 102, respectively. Output control signal 11 of multiplexer 102
3 shows the case where the mark waveform is convex upward and the slice level above the base is used (see A in FIG. 3), and the non-inverted output is used when the mark waveform is convex downward and the slice level below the base is used (see FIG. (See B of 3) controls to output an inverted output. The mark waveform thus selected is input to the adder 103. Here, a 16-bit adder is used. The other input of the adder 103 is the addition memory 104.
However, a multiplexer 105 is provided between them and a control signal 112 is used to add 0 when no addition is performed or for the first waveform of addition. A shift register 108 is connected to the output of the adder 103, and if it is desired to avoid a base level increase due to addition or an addition overflow due to the control signal 114, right shift by one bit and the waveform is halved. However, even if it is desired to reduce the waveform to 1/2, no shift is performed on the first waveform of addition. Shift register 1
The output of 08 is input to the addition memory 104 at the same time as it is input to the edge detection circuit 107. Addition memory 104
The address of is incremented for each sampling,
It is connected to a counter 106 that is reset to 0 when the collection of one waveform data is completed. Edge detection circuit 10
Reference numeral 7 may be a hardware arithmetic circuit or a circuit that is arithmetically processed by a processor such as a DSP. As shown in FIG. 3, the contents of processing in this circuit are, when the waveform is convex upward A, a point 303 which passes the slice level 302 with respect to the mark waveform 301 is extracted as an edge, and its position is the start point of the waveform data. It stores in the memory what number it is from. The same applies to the case where the waveform is convex downward. In addition, this circuit detects how many waveforms have a specified number of edges, and when the number of specified waveforms is reached, a signal indicating that there is a mark is output. Since the example of A is a waveform having four edges, for example, if five detection conditions are specified, a signal indicating that there is a mark is issued when five waveforms of A are collected. This signal is shown as signal 109 in FIG.

Alternatively, as shown in C, for example, when a waveform having four edges is a mark waveform, there are a specified number of waveforms satisfying this condition and the signal amplitude range 305.
When the saturation point 306 is generated, the mark is set as a condition. According to this condition, the designation of the number of waveforms having the designated number of edges is reduced to about several, and the slice level 3
If 02 is set at a high position in the amplitude range 305 of the signal, the success rate of existence detection is high even for a waveform with low contrast and low S / N. Of course, the shift register 108
Is set to no shift. In this case, the adder 103
OR 1 of overflow signal 111 and signal 109 of
10 may be used as the mark presence detection signal. Note that FIG.
The arrow 304 indicates the scanning width of the electron beam, that is, one waveform length. In addition to issuing the presence detection signal, the edge detection circuit 107 also has a function of storing in the memory 117 what number of data of which scanning waveform has an edge. This so-called edge detection method is known. Therefore, it will not be described in detail here.

On the other hand, the edge detection circuit 107 only expands the number of processing bits of the conventional circuit from 12 bits to 16 bits, and the processing time is not increased by processing the added waveform. In addition, the processing time due to addition to the adder circuit is within 1 μS even when all devices are configured with the 74LS series, and is sufficiently absorbed within the sampling cycle of 15 μS that is limited by the response characteristics of the detector. No increase in processing time occurs. That is, the processing time does not increase as compared with the conventional method.

The mark presence detection signals 110 and 109 issued by the above processing and the position information of the mark waveform stored in the memory 117 are transmitted to the control computer 213 via the interface circuit not shown in FIG. Is taken into.

[0012]

As described above, according to the present invention, it is possible to improve the success rate of the presence detection of the alignment mark especially by cumulatively adding the alignment mark waveforms and performing the edge detection processing for each addition waveform. . Further, with respect to position detection, detection reproducibility can be improved. Further, compared to the conventional method, the processing time according to the present invention does not increase.

[Brief description of drawings]

FIG. 1 is a functional block diagram for explaining the present invention.

FIG. 2 is a schematic configuration diagram of the entire apparatus.

FIG. 3 is an explanatory diagram of processing contents of an edge detection circuit.

[Explanation of symbols]

101 ... Flip-flop, 102, 201 ... Mirror body, 1
03 ... Adder, 104, 117 ... Memory, 105 ... Multiplexer, 106 ... Counter, 107 ... Edge detection circuit, 108 ... Shift register, 109, 110 ... Presence detection signal, 112, 113 ... Control signal, 114 ... A / D Converter, 205 ... Sample, 207 ... Semiconductor detector, 210 ...
Signal processing unit, 213 ... Control computer, 301 ... Mark waveform, 302 ... Slice level, 303 ... Edge, 306
… Saturation point of addition.

Claims (5)

[Claims] 1. An electron gun for generating an electron beam, an electron optical system for projecting the electron beam emitted from the electron gun onto a sample surface, and deflection control for scanning the electron beam on the sample surface. A detector for detecting backscattered electrons or secondary electrons generated when a system and a semiconductor wafer fixed on the sample surface or a registration mark on a mask are scanned with an electron beam; and a signal from the detector is amplified, A signal processing system including an analog processing unit for limiting a frequency band, an A / D conversion unit for converting the signal into a digital amount, and a digital processing unit for arithmetically processing the digital amount signal, and the electronic optical system, An electron beam drawing including a data control system for collectively controlling the deflection control system, the signal processing system, and a stage control system for moving the sample to perform high-speed and accurate drawing control, and a control computer for the data control system. When the alignment mark position is detected in the device, the mark waveforms obtained by scanning the alignment mark with an electron beam are cumulatively added, and the position detection on the waveform that exceeds the slice level specified in advance for each addition, so-called An electron beam drawing apparatus characterized in that a mark position is detected by performing edge detection by hardware calculation or software processing. 2. A mark waveform having a preset number of edges by cumulatively adding scanning signals when performing the presence detection of alignment marks and performing the edge detection for each addition by hardware calculation or software processing. But,
The electron beam drawing apparatus according to claim 1, wherein a mark is present when a designated number is found. 3. A mark waveform having a preset number of edges, which is obtained by cumulatively adding scanning signals when detecting the presence of alignment marks, and performing the edge detection by hardware calculation or software processing for each addition. 2. The electron beam drawing apparatus according to claim 1, wherein the mark is present when the specified number or more are found and the added waveform is saturated (overflowed). 4. The alignment mark presence detection method according to claim 3, wherein when the mark waveform is convex upward and the slice level is set above the waveform base, normal cumulative addition is performed and the mark waveform is shifted downward. An electron beam drawing apparatus, which is convex and which performs cumulative addition by inverting all bits of the detected waveform when the slice level is set below the waveform base. 5. The alignment mark position detection according to claim 1, wherein the addition waveform is always set to 1/2 to perform cumulative addition and edge detection, whereby the position can be detected without increasing the base of the mark waveform due to addition and addition overflow. Electron beam writer.