JPH0724256B2 - Size measuring device - Google Patents

Description

The present invention relates to a beam size measuring device, and more particularly to a beam size measuring device capable of accurately measuring the size of a beam used in a charged particle beam device or the like. Regarding the device.

(Prior Art) A charged particle beam drawing apparatus is an apparatus for drawing a predetermined pattern on a material placed on a material stage by scanning a beam emitted from a charged particle source in a two-dimensional direction. As this type of apparatus, an electron beam drawing apparatus, a charged particle beam drawing apparatus, or the like is used. In recent years, this type of beam drawing apparatus has been attracting attention because it can directly draw a highly accurate chip pattern on a wafer in the field of semiconductor manufacturing. When performing such beam writing, since the chip pattern is an extremely minute pattern, it is necessary to measure the beam width in advance and calibrate it to an optimum beam size.

Conventionally, the following method has been used as a method for obtaining the beam size. That is, first, a mark M as shown in FIG. 4A is formed on the material stage,
The mark M is scanned with a beam Bi having a diameter smaller than the width of the mark M. At this time, the beam Bi crosses the mark M in the direction of the arrow in the figure, so that a reflected signal is emitted from the mark M. If the beam size is large here, the mark M
The time required to pass the edge of the mark M becomes long, and the time required to pass the edge of the mark M becomes short when the beam size is small. From the above, the rise time Δ of the detection signal
W has a value corresponding to the beam size. When the beam size is actually obtained, this detection signal is secondarily differentiated to facilitate the beam size.

FIG. 5 is a diagram showing a configuration example of a conventional beam size measuring device. In the figure, 1 is a mark placed at a specific position on a material stage (not shown), and 2a and 2b are reflection signal detectors (hereinafter simply referred to as detectors) arranged to face the mark 1 respectively. Reference numeral 3 is an adder for adding the outputs of these detectors 2a and 2b. Reference numeral 4 denotes a quadratic differential circuit for quadratic differentiating the output of the adder 3, reference numeral 5 denotes an absolute value circuit for taking the absolute value of the output of the secondary differential circuit 4, and reference numeral 6 denotes the output of the absolute value circuit 5. It is a gate circuit that receives and outputs the pulse counted by the gate width corresponding to the beam size. The operation of the circuit thus configured will be described below.

When the beam Bi is scanned in the direction of the arrow in the figure, a reflected signal is emitted from the mark 1 and the reflected signal is generated by the pair of detectors 2a, 2b.
Detected in. The outputs of the pair of detectors 2a and 2b are added by the adder 3. FIG. 6A shows the added detector output. This addition output is differentiated twice by the subsequent secondary differentiation circuit 4 and then converted into an absolute value by the absolute value circuit 5. FIG. 6B shows the output of the absolute value circuit 5. Gate circuit 6
Receives the output of the absolute value circuit 5, creates a gate as shown in (c) from the peak and the peak of the absolute value signal, counts the pulses by this gate width, and outputs the pulse as shown in (d). Create a count signal. Then, this pulse count is output from the gate circuit 6 as a signal corresponding to the beam size. This output is multiplied by a predetermined coefficient to convert the number of pulses into a beam size, which is the final answer.

(Problems to be Solved by the Invention) Even in the conventional apparatus, the beam size can be obtained relatively accurately. However, in this apparatus, the secondary differentiating circuit 4 is used to differentiate the detection signal twice. Therefore,
If the detection signal contains noise, this secondary differentiation circuit 4
Since the noise also differentiates, the width of the gate circuit 6 changes when the gate is formed, which causes an error in the measurement result. In order to reduce the influence of such noise on the differentiating circuit, calculation up to the third derivative is also performed, but it is not so effective.

The present invention has been made in view of such points,
It is an object of the present invention to realize a size measuring device with a simple configuration that can accurately measure the beam size and the mark width size without being affected by noise.

(Means for Solving Problems) The present invention for solving the above problems has a peak corresponding to an edge portion of a mark based on a reflection signal emitted from the mark when a beam scans the mark. The peak detection circuit comprises: a signal generating means for generating a signal; an autocorrelation circuit for autocorrelating the output of the signal generating means; and a peak detection circuit for detecting the peak of the signal having the autocorrelation. The width from the reference position to the peak is obtained based on the output, and the size of at least one of the beam and the mark width is calculated from the width thus obtained.

(Operation) In the device of the present invention, the signal generating means generates the signal having the peak corresponding to the edge portion of the mark based on the reflection signal emitted from the mark when the beam scans the mark, and the autocorrelation The circuit autocorrelates the output of this signal generating means. The peak detection circuit detects the peak of the autocorrelated signal. Then, the width from the reference position to the peak is obtained based on the output of the peak detection circuit, and at least one of the beam width and the mark width is calculated from the thus obtained width.

(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. In FIG. 5, the same parts are designated by the same reference numerals. In the figure, 7 is an A / D converter for converting the output of the absolute value circuit 4 into digital data, and 8 is a memory section for storing the output of the A / D converter 7. Reference numeral 9 is an autocorrelation circuit that sequentially reads out the data stored in the memory unit 8 to perform an autocorrelation operation, and 10 is a peak detection circuit that detects the peak based on the output of the autocorrelation circuit 9. The operation of the apparatus thus configured will be described below with reference to the timing chart shown in FIG.

The beam Bi scans the mark 1, the reflected signals from the mark 1 are detected by the detectors 2a and 2b, and these detected signals are secondarily differentiated by the second differentiating circuit 4 and then absolute by the absolute value circuit 5. Quantify. The operation of the circuit so far is the same as that of the circuit shown in FIG. 5, that is, the detector output as shown in FIG. Value circuit 5
Is converted into an absolute value and becomes an absolute value signal as shown in (b). The A / D converter 7 samples the output of the absolute value circuit 5 at a constant cycle and converts it into digital data. The converted digital data is sequentially stored in the memory unit 8.

The autocorrelation circuit 9 receives data D (I), D (I
+ J) (I: memory address, J: address difference) is read out, and the autocorrelation operation of the following equation is performed.

Here, R (J) is an autocorrelation function and N is the number of data points. FIG. 2C shows the autocorrelation output waveform calculated by the above equation. The peak detection circuit 10 searches for the peak from the autocorrelation function R (J) calculated by the autocorrelation circuit 9. Here, the peak searched by the peak detection circuit 10 is R
The peak that can be (O) is the first peak, and is the second peak P that is formed when J increases.

The peak detection circuit 10 obtains the address of the peak point and calculates the beam size from the formula shown below.

Beam size = (scan length for 1 point of address) × (address of peak point) (2) According to the present invention, the method of obtaining the gate width according to the beam size is not used, and the autocorrelation function is used. Has the effect of attenuating the non-periodic signal of the original waveform, so that the beam size can be accurately obtained without being affected by noise even in an environment where noise is generated.

In the above description, the case where the beam size is measured has been described, but the device of the present invention can also be applied to the measurement of the mark width size. That is, for example, when the difference between the outputs of the detectors 2a and 2b arranged in the scanning direction above the step mark having a concave sectional shape is obtained, a detection signal (difference signal) as shown in FIG. can get. When this is converted into an absolute value by the absolute value circuit 5, a waveform as shown in (b) is obtained. This signal is similar to the one obtained by quadrically differentiating the beam size signal and converting it into an absolute value (see FIG. 2B). In this case, a subtracter is used instead of the adder 3, and the secondary differentiating circuit 4 is omitted and the absolute value circuit 5 is directly inserted.

Next, the absolute value signal thus obtained is converted into digital data by the A / D converter 7 and given to the autocorrelation circuit 9. As a result, the autocorrelation circuit 9 outputs an autocorrelation signal as shown in FIG. The distance from the origin O of this signal to the second peak point P corresponds to the mark width W.

In the above-described embodiment, the case where the absolute value of the detection signal is taken and then converted into digital data has been described as an example, but the absolute value conversion is not always necessary.

(Effects of the Invention) As described in detail above, in the present invention, the signal generating means generates the peak corresponding to the edge portion of the mark based on the reflection signal emitted from the mark when the beam scans the mark. Is generated and the autocorrelation circuit takes the autocorrelation of the output of this signal generating means. The peak detection circuit detects the peak of the autocorrelated signal. Then, the width from the reference position to the peak is obtained based on the output of the peak detection circuit, and at least one of the beam width and the mark width is calculated from the thus obtained width.

As described above, in the present invention, the autocorrelation of the output of the signal generating means that generates a signal having a peak corresponding to the edge portion of the mark based on the reflected signal emitted from the mark when the beam scans the mark is calculated. As a result, a signal having a peak at a position corresponding to the peak portion in the output of the signal generating means and having no influence of noise is obtained, and the size of the beam or mark width can be accurately measured. A measuring device can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a timing chart showing the operation of each part, FIG. 3 is a timing chart showing an application example of the present invention, and FIG. 4 is a conventional beam size measurement. FIG. 5 is a diagram showing a configuration example of a conventional device, and FIG. 6 is a timing chart showing the operation of each part. 1 …… mark, 2a, 2b …… detector 3 …… adder, 4 …… second derivative circuit 5 …… absolute value circuit, 7 …… A / D converter 8 …… memory section, 9 …… self Correlation circuit 10 ... Peak detection circuit

Claims (3)

[Claims] 1. A signal generating means for generating a signal having a peak corresponding to an edge portion of a mark based on a reflection signal emitted from the mark when the beam scans the mark,
An autocorrelation circuit for taking an autocorrelation of the output of the signal generating means and a peak detection circuit for detecting a peak of the signal having the autocorrelation are provided, and the peak is detected from a reference position based on the output of the peak detection circuit. And a size of at least one of the beam width and the mark width is calculated from the width thus obtained. 2. A signal generating means comprises a detector for detecting a reflection signal emitted from the mark when the beam scans the mark, and a differentiating circuit for differentiating the output of the detector,
The output of the differentiating circuit is input to the autocorrelation circuit, the width from the reference position to the peak is calculated based on the output of the peak detection circuit, and the beam size is calculated from the width thus calculated. The size measuring device according to claim 1, wherein 3. Two detectors which are respectively arranged in a beam scanning direction and detect a reflection signal emitted from the mark when the beam scans the mark, and a difference signal between outputs of the two detectors is generated. The signal generating means is composed of the difference signal generating means, the output of the difference signal generating means is input to the autocorrelation circuit, and the width from the reference position to the peak is obtained based on the output of the peak detection circuit. The size measuring device according to claim 1, characterized in that the mark width size is calculated from the obtained width.