JPH0261133B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mark position detection method in an electron beam exposure apparatus.

In general, mark position detection in an electron beam exposure device involves scanning a mark previously provided on a sample many times with an electron beam, and using the backscattered electrons, so-called reflected electrons, obtained at that time, as shown in Figure 1a. to detect the position of the mark above. The detectors X ⁺ and X ^- that detect this backscattered electron are
They are arranged above the opposing ends of the mark, and their output waveforms are ^{Ex +} _{and Ex} ^- as shown in FIGS. 1b and 1c, respectively.

Conventionally, in mark position detection, as shown in Fig. 1d, the difference between the above two signals _Ex ⁺ and _Ex ^- , that is, a difference signal E _s is created, and an appropriate slice level Sl is set for the difference signal. _h and Sl _l are provided, and these Sl _h and Sl _l are E _s
The position at the moment of passing (so-called edge information) e _s1
~e _s4 was extracted, and then the average value of the four values was calculated, which was used as the position of the mark in the X direction. The position in the Y direction is also determined by a similar method, in which the mark is scanned in the Y direction with a beam and the difference signal obtained as a result is used to determine the position of the mark in the Y direction.

As can be seen from the above description, conventionally, the detection accuracy of the determined mark position depends on the accuracy (reproducibility) of the extracted mark edge information e _s1 to e _s4 . Incidentally, the accuracy of mark edge information becomes better as the slope of the E _s waveform becomes steeper. However, as can be seen from Figure 1(d), in the past, edge information e _s1 was obtained by using the gentle slope portions of the E _x ⁺ and E _x ^- waveforms.
~e _s4 is extracted, which has the disadvantage that the accuracy of mark position determination using the difference signal deteriorates.

The present invention has been made with attention to this point, and provides a mark position detection method in an electron beam exposure apparatus that enables highly accurate mark position detection.

In order to achieve the above object, in the present invention, alignment marks provided on a sample are scanned with an electron beam, and electrons secondarily emitted from the marks are
Detection is performed by a detection means arranged symmetrically with respect to the optical axis, and only position data (edge information) obtained from a steep waveform portion of the output waveform of the composite output signal from the detection means is selectively detected. The mark position is determined by extracting the mark and using it.

Hereinafter, the present invention will be explained with reference to Examples.

FIG. 2 shows a waveform diagram of the sum (synthesis) signal E _a of the output signals Ex ⁺ and Ex ⁻ from the detectors _X ⁺ and _X ⁻ shown in FIG. 1. In the figure, e _a1 to e _a8 are this sum signal
Set appropriate slice levels Sl _h and Sl _l for E _a ,
This Sl _h indicates the position (edge information) at the moment Sl _l crosses E _a .

Edge information extracted in this way e _a1 to e _a8
Of these, edge information e _a5 to e _a8 that utilize the steep part of the E _x ⁺ and E _x ^- (see Figure 1) waveforms, and e _a1 to e _a4 that use the gentle part of the waveform. Since the edge information is mixed, if the mark position is simply determined using all of these edge information, the accuracy will be poor. Therefore, in the present invention, the mark position is determined using only the edge information from the steep part of the waveform of E _a , and there are two methods for this purpose as described below.

First, as shown in Fig. 3a, the width d of the step mark is narrowed and the electron beam is scanned over it to obtain the respective output signals E _x ' ⁺ and E from the detectors X ⁺ and X ^- . _x ′ ^-
Edge information obtained from the steep waveform part of the waveform of the sum signal E _a ' (Fig. 3 d) of (Fig. 3 b, c)
This is a method of extracting only e _a ′ ₁ to e _a ′ ₂ and determining the mark position.

The width d' at this time is mainly determined by the energy of the incident electrons, but for example, in an electron beam exposure apparatus with an accelerating voltage of 30 kV, a width of 5 μm or less is effective.

The second is e _a1 to e _a4 of the edge information in Figure 2.
Using the difference in reproducibility of the positions of e _a5 to e _a8 , e _a5 to
Data processing and extraction of only the edge information of e _a8 ,
After that, the position of the mark is determined to obtain the average value of e _a5 to e _a8 . In other words, looking at the line-to-line variation of each edge information obtained by scanning the step mark n times, e _a1i to e _a4i (i = 1 to n) have large line-to-line variations, but e _a5i to e For _a8i , the variation between each line is as above e _a1i ~e _a4i
It is small compared to the variation in Therefore, if we use this difference in variation between the two, e _a1i ~e _a4i and e _a5i ~
e It becomes possible to separate _{the a8i} .

Note that the slice level used in the two methods described above is, for example, the maximum value of the mark detection signal,
It is possible to determine Sl _h and Sl l shown in Fig. 2 or Sl _{l '} shown in Fig. 3 d by determining the minimum value and the signal value (base level) reflecting the board _part of the mark. can. How these slice levels are used is determined by the shape of the mark to be detected, how the mark detection signal is used, etc.

_Furthermore , in the present invention ^, when the target mark has ^a _convex shape as shown in FIG. ⁴ , the output waveforms from ^the detectors The sum signal is
E _a ″, so the slice level needs to be Sl″ _h . Furthermore, it goes without saying that the present invention can be applied effectively even when a large number of target marks are lined up as shown in FIGS. 5a and 5b.

FIG. 6 is a block diagram showing a specific configuration of an embodiment of the present invention. In the figure, 1 is an electron beam, 2 is an alignment mark provided on the sample, such as a step mark as shown in the figure, and 3 is an electron secondarily emitted from the mark 2 by electron beam irradiation, such as A detector for detecting reflected electrons, 4 a current-voltage converter, 5 and 6 X and Y deflectors for scanning the electron beam in the X direction or Y direction,
7 and 8 are digital-to-analog converters (D/A converters); 9 is an adder for creating the sum signal E _a '; 10 is an analog-to-digital converter (A/D converter);
11 is a latch memory for establishing input signal data; 12 and 13 are registers for temporarily storing deflection data; 14 is a comparator for extracting edge portions; 15 is a register for storing slice levels;
16 is a memory for storing positional information (so-called edge information) when the edge portion is extracted, that is, the X and Y deflection positions; 17 is an arithmetic circuit for determining the mark position; 18 is this circuit system This is a control circuit for controlling. Note that the detector 3 is
Although the figure only shows a pair of detectors arranged in one direction, in this example, a pair of detectors are arranged in each of the X and Y directions so as to be positioned symmetrically with respect to the optical axis. It is set up. Also, mark 2
The shape does not necessarily have to be a stepped shape as shown in the figure, but any shape from which edge information can be obtained can be applied.

In this embodiment, in order to scan the electron beam in the X direction, deflection data is sequentially transferred from the control circuit 18 to registers 12 and 13, and the data is transferred to
The above scanning is performed by performing A conversion and moving the beam to the target position one after another. Also sum signal
To capture E _a ', the E _a ' signal is A/D converted in synchronization with the movement of the beam position at each point, digitized, and sequentially temporarily stored in the latch memory 11. This digital signal is converted to a slice level by a comparator 14.
A signal 100 corresponding to the edge portion is detected by comparing with Sl _l ′. The above Sl _l ' is transferred from the control circuit 18 to the register 15 in advance. When the signal 100 is detected, the beam deflection data 101 and 102 at that time is taken into the memory 16 in synchronization with the signal.

Necessary edge information in the X and Y directions is acquired by the method described above. When the required number of scans is completed in this way, the edge information of the mark extracted for each scan line is stored in the memory 16, so the control circuit 18 instructs the mark position determination circuit that calculates the position of the mark. to determine the position of the mark to be processed.

That is, in the position determining circuit 17, the control circuit 18
Upon receiving the command, the edge data group stored in the memory 16 is rearranged. In other words, the detected edge data are rearranged at positions on each scanning line. At this time, if the first method described above is adopted as the edge data processing method, it is checked whether the number of edge data detected in each line is two, for example, as in the example shown in Fig. 3d, and if there are two, then If they are not equal, remove all data belonging to that line. Thereafter, a simple average of all remaining edge data is calculated and used as the mark position.

Furthermore, when the second method described above is adopted as the edge data processing method, the arranged edge data group is divided into a data group with good reproducibility and a data group with poor reproducibility. Next, it is confirmed that the number of edge data detected in each line is, for example, 6, and if it is not equal to 6, all data belonging to that line are removed. Convolution processing is performed on the remaining data group to examine mutual correlation. The range of integration when convolution processing is performed at that time is determined to be about 2 to 6 times the variance of the edge data group with good reproducibility. After that, a new slice level is created to extract only data groups with good reproducibility. Thereafter, a simple average is performed within each data group, one representative edge data is extracted from each group, and finally, after checking the number of representative edge data, the simple average is determined and used as the mark position.

As described above, according to the present invention, position data obtained from a steep waveform portion of the output waveform is based on a composite output signal from at least a pair of detectors arranged symmetrically with respect to the optical axis. By using this method, the position of a mark can be detected with extremely high precision, and its effect is great when applied to various charged particle beam devices such as electron beam lithography devices. In addition, although the above embodiment mainly describes the detection of reflected electrons emitted from a mark by electron beam irradiation, the present invention is essentially applicable to secondary electrons, transmitted electrons, etc. It is. Furthermore, it is not necessary to provide a pair of detectors for detecting this in each of the X and Y directions as in the above embodiment, but it is also possible to provide a pair of annular detectors axially symmetrical to the optical axis. In that case, the adder 9 in FIG. 6 becomes unnecessary.

[Brief explanation of drawings]

FIG. 1 is a waveform diagram explaining conventional mark position detection, FIGS. 2 and 3 are diagrams explaining the principle of the present invention, and FIG. 4 shows an example of application when the mark is convex. FIG. 5 is a diagram showing a plurality of marks, and FIG. 6 is a block diagram explaining an embodiment of the present invention. In the figure, 1...electron beam, 2...mark, 3...detector, 5, 6...X, Y deflector, 9
... Adder, 11 ... Latch memory, 14 ... Comparator, 16 ... Memory, 17 ... Arithmetic circuit, 18
...control circuit.

Claims (1)

[Claims] 1. An alignment mark provided on a sample is scanned with an electron beam, and electrons secondarily emitted from the mark are transmitted to at least one positioning mark arranged symmetrically with respect to the optical axis. Only the position data obtained from the steep waveform part of the output waveform of the composite sum signal is detected by a pair of detectors, and is obtained by comparing the slice level with the composite sum signal of the signals detected by the detectors. 1. A mark position detection method in an electron beam exposure apparatus, characterized in that the position data of the mark is selectively extracted, and the position of the mark is determined based on the selectively extracted position data. 2. A mark position detection method in an electron beam exposure apparatus according to claim 1, wherein the mark is a step mark having a width of 5 μm or less.