JPH0682607B2 - Mark position detector - Google Patents

Description

The present invention relates to a mark position detecting device, and more specifically, to a mark position detecting device for positioning a material placed on a material stage by a beam drawing device or the like. Regarding the device.

(Prior Art) An electron beam drawing apparatus and a focused ion beam drawing apparatus perform beam drawing of a predetermined pattern on a material placed on a material stage. When drawing a predetermined pattern of a material with this type of beam drawing device, the pattern data is output and drawn in an open loop, so if the initial position is misaligned, all patterns will be misaligned thereafter. It will be. Therefore, in this type of beam drawing apparatus, the setting of the initial position of the material is extremely important. Various methods are used for setting the initial position of the material.

A mark position detection method, for example, is used as an initial position setting method for such a material. This mark position detection method forms a mark at a predetermined position on the material or material stage,
Beam scanning is performed on the mark. The mark position is detected by utilizing the fact that the information of the reflected signal such as the reflected electrons emitted from the mark when the beam is applied to the mark is different from the reflected signal around the mark.

FIG. 5 is a diagram showing a configuration example of a conventional mark detection device. The beam Bi is deflected by the deflector 1 and scanned in the scanning direction shown in the figure. When the mark 2 is irradiated with this beam Bi, the reflected signal R is emitted from the mark 2. The emitted reflected signal R is detected by the reflected signal detector 3 and converted into an electric signal. Here, for example, the reflected signal detector 3 is divided into two units, a unit 3a (channel 1) and a unit 3b (channel 2), which respectively output detection signals e1 and e2.

The outputs e1 and e2 of the units 3a and 3b enter the arithmetic circuit 4, and the arithmetic circuit 4 calculates the difference between the e1 and e2. FIG. 6 is a timing chart showing the operation of each part. If mark 2 is in the position shown in (a),
The difference signal as shown in (b) is obtained from the arithmetic circuit 4. As is clear from (a) and (b), the center between the positive and negative peaks indicates the mark position.

However, since the peak position is not clear with the signal shown in (b) as it is, this difference signal is put into the differentiating circuit 5 and differentiated. As a result, the differential circuit 5 obtains a differential waveform in which the peak is emphasized as shown in (c). The gate circuit 6 receives the differentiated output and receives the mark 2 from the reference position K.
A gate width corresponding to the center position of is created, and pulses counted by this gate width are output.

Here, the operation of the gate circuit 6 will be described in detail. In FIG. 6 (c), if the distance from the reference point K to the first gate is A and the distance to the second gate is B, the distance to the center position P of the mark (mark position) L is The L = A + (B−A) / 2 gate circuit 6 given by the following formula creates a gate having a width based on the above formula,
The pulse counted by this gate width is output. (D) is the output (gate signal) of the gate circuit 6.

(Problems to be Solved by the Invention) Even with the apparatus shown in FIG. 5, the mark position can be accurately obtained in an environment without noise. Once the mark position is obtained, the initial position of the material can be corrected based on that position. However, when the device is placed in an environment where noise is generated, the differentiating circuit 5 also differentiates the noise superimposed on the detection signal, and the output waveform thereof contains much noise as shown in FIG. It becomes a waveform including. Therefore, the position of the gate constantly moves as shown in (b), and accurate positioning becomes impossible. Further, if there is noise, the level of the noise exceeds the threshold value at other points, and a gate signal is generated, resulting in malfunction. As described above, since the conventional method is vulnerable to noise, there is a demand for an apparatus that can process a signal with a poor SN ratio such as a thick resist on a mark.

The present invention has been made in view of such points,
The purpose is to realize a mark position detection device that is resistant to noise.

(Means for Solving the Problems) The present invention which solves the above-mentioned problems is a reflection signal detector for detecting a reflection signal reflected from a mark irradiated with a beam, and each division of the reflection signal detector. An arithmetic circuit that receives the output of each unit to obtain a sum signal or a difference signal, an impulse response arithmetic circuit that receives the arithmetic circuit output and performs an impulse response arithmetic operation, and the maximum and minimum values from the output of the impulse response arithmetic circuit A maximum value / minimum value detection circuit for detecting the maximum value / minimum value. It is characterized in that it is configured to obtain it as width information.

(Operation) Impulse response calculation is performed instead of the differentiating circuit to emphasize the center position of the mark and the peak of the signal from the detection signal.

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

FIG. 1 is a block diagram showing an embodiment of the present invention. The same parts as those in FIG. 5 are designated by the same reference numerals. The process up to the point where the signals for two channels detected by the reflected signal detector 3 are input to the arithmetic circuit 4 and two detection signals are taken out from the arithmetic circuit 4 is the same as in FIG. Reference numeral 11 is an impulse response operation circuit that receives a difference signal from the operation circuit 4 and performs an impulse response operation. Reference numeral 12 is an output of the impulse response operation circuit 11 and detects maximum and minimum values thereof. Circuit. Then, the mark position and the mark width can be obtained from the output of the maximum / minimum value detection circuit 12. The operation of the apparatus thus configured will be described below.

Similar to the case of FIG. 5, two signals from the arithmetic circuit 4
The difference signal between e1 and e2 is output. Here, in order to explain the subsequent processing, the difference signal is the digital data D.
(I) (where I is an address and I = O to N1, N is the number of data points). Digitization of such a signal can be easily realized by using, for example, an A / D converter. Impulse response calculation circuit 11
Receives the digitized difference signal D (I) and performs the following calculation.

Here, the impulse response will be described.
The impulse response Z (t) is generally defined as follows in the field of signal processing.

Where y (t) is a signal, and equation (2) is Satisfy the condition of. Z (t) represented by the equation (2)
Is a response normally used to investigate the response of a system, and the form of h (t) varies depending on the system.

As h (τ), a function y (+ τ) inverse in time with respect to y (t−τ) is generally used.
Let y (t + τ) be chosen as (τ). or,
If the section of equation (2) is W, Becomes Here, if equation (4) is digitally expressed, And becomes the same as the expression (1).

FIG. 2 is a diagram showing operation waveforms of each part. (A) is the difference signal D (I) output from the arithmetic circuit 4, and (B) is the output waveform of the impulse response arithmetic circuit 11. This impulse response Z (I) acts to find the center of the mark from the mark signal. This Z (I) does not have to be calculated for all the regions of I, but may be calculated for approximately half of N (near the center of the difference signal and one region on one side).

The maximum / minimum value detection circuit 12 receives the output Z (I) of the impulse response calculation circuit 11 and detects the maximum and minimum values. As shown in FIG. 2 (b), if the I point corresponding to the maximum value of Z (I) is I _MAX and the I point corresponding to the minimum value is I _MIN , I _MIN indicates the mark position by 2 × 1I _MIN. -I _MAX 1 represents the mark width. That is, the difference between I _MIN and I _MAX is W × 2 × W
Indicates the mark width. Obtaining the mark width is significant for the purpose of checking whether the mark position information captures a signal such as dust that is not the original mark.

Next, it is proved that I _MIN represents the mark position and 2 × 1 I _MIN −I _MAX 1 represents the mark width. Now, consider the impulse response represented by the equation (5) based on the difference signal y (i) as shown in FIG. The expression (5) is a method in which i is first fixed, and the data comrades apart from each other in both directions by j with respect to the i are multiplied. This result is close to the image of obtaining the center of gravity of a signal. This operation also serves to reduce noise that is uncorrelated with signals such as random noise. Therefore, as the response, a curve of Z (i) as shown in (b) is obtained, and in the case of the data of + and-both poles with respect to the baseline like the difference signal, the minimum value (MIN) The center of the mark appears. or,
The points of both the + and-peaks of y (i) of the difference signal are Z (i)
You can see that it appears in the MAX part. Therefore, 1MAX address-M
The IN address 1 × 2 represents the mark width.

In the above description, the case where the arithmetic circuit 4 calculates the difference between two signals has been taken as an example, but the present invention is not limited to this. You may make it take the sum signal of two signals.
The relationship between the sum signal and the impulse response Z (i) in this case is as shown in FIG. (I) is the sum signal y (i), and (b) is the impulse response Z (i). Thus, y (i) is +/- with respect to the baseline l.
Try to divide it into In this case, the response is as shown in (b), and the point of maximum value MAX is the center of the mark, and the point of minimum value MIN is near the edge of the mark. Therefore, the 1MAX address-MIN address 1x2 also represents the approximate mark width.

(Effect of the Invention) As described in detail above, according to the present invention, the impulse response calculation is performed on the difference signal or the sum signal of two signals from the mark without passing through the differentiating circuit, and the mark position is calculated from the peak value. Since the mark width is obtained, it is possible to realize a mark position detecting device that is resistant to noise.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing operation waveforms of respective parts, and FIG. 3 is a diagram showing that a mark position and a mark width are obtained from impulse response calculation. FIG. 4, FIG. 4 is a diagram showing operation waveforms of each part when the detection signal is a sum signal, FIG. 5 is a diagram showing a configuration example of a conventional device, FIG. 6 is a view showing operation waveforms of each part, and FIG. The figure shows the operation when noise is superimposed. 1 ... deflector, 2 ... mark 3 ... reflection signal detector, 4 ... calculation circuit 11 ... impulse response calculation circuit 12 ... maximum value / minimum value detection circuit

Claims (1)

[Claims] 1. A reflection signal detector for detecting a reflection signal reflected from a mark irradiated with a beam, and an arithmetic circuit for receiving an output of each division unit of the reflection signal detector to obtain a sum signal or a difference signal. And an impulse response operation circuit that receives the output of the operation circuit and performs an impulse response operation, and a maximum value / minimum value detection circuit that detects the maximum value and the minimum value of the impulse response from the output of the operation circuit, A mark characterized in that the minimum value or the position giving the maximum value detected by the maximum value / minimum value detecting circuit is obtained as the mark position, and the difference between the positions giving the maximum value and the minimum value is obtained as the information of the mark width. Position detection device.