JPH02226001A - Method for detecting pattern edge - Google Patents

Abstract

PURPOSE:To enhance the reproducibility of measurement by readjusting the focus of laser beam or electron beam when the waveform of a reflected signal or that of a secondary electron signal is unsimilar to the waveform of a reference signal to perform re-detection. CONSTITUTION:Prior to measurement, the waveform SA of a reference signal corresponding to a pattern edge is stored in a reference signal waveform memory means 1. At the time of measurement, laser beam is generated by a laser beam generating/scanning means 3 to be projected on an objective pattern and a reflected beam signal is detected by a detector 5 to obtain a reflected beam signal waveform SB which is, in turn, corrected by an amplitude correction means 6 so that the difference between the base line and peak value of the reflected beam signal waveform SB coincides with that of the reference signal waveform SA to obtain a signal SB. Then, the difference between the reference signal waveform SA and the waveform of the signal SB' is calculated according to a convolution method by a signal waveform comparing means 7 and, when the difference is larger than a prescribed value, the focus of the laser beam generating/scanning means 3 is adjusted through a focus matching mechanism 4 and the difference is set to a prescribed value before measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pattern edge detection method suitable for use in a fine dimension measuring device used in semiconductor manufacturing processes and the like.

[Prior Art] Generally, in a laser beam scanning type micro-dimensional measuring device,
After focusing on a reference plane near the target pattern, a preset focus offset is performed, the target pattern is scanned with a laser beam, and pattern edges can be detected from the reflected optical signal waveform obtained by this scanning. carried out,
The dimensions and shape of the target pattern are measured.

In addition, in an electron beam scanning type fine dimension measurement device, pattern edges are detected from the secondary electron signal waveform obtained by scanning an electron beam instead of a laser beam, and the dimensions and shape of the target pattern are measured. .

[Problems to be Solved by the Invention] By the way, the reflected light signal waveform obtained in a laser beam scanning type micro-dimensional measuring device has: ■Focusing accuracy (focusing accuracy is affected by the surface condition of the reference surface); ■
Relative positional relationship in the Z-axis direction between the focusing position and the target pattern (if there is a step near the target pattern, the stage position reproducibility accuracy.

(Sometimes the focusing position is at the top of the step and sometimes it is at the bottom of the step within the range), ■ Focus shift reproducibility after focusing, etc. This causes a decrease in the reproducibility of measured values. Ta.

In addition, in the case of an electron beam scanning type microdimensional measurement device, focusing is performed on a plane with a certain area,
The reference plane thus obtained varies slightly with respect to the target pattern. Furthermore, the waveform of the secondary electron signal is distorted due to the charge-up phenomenon, which causes a decrease in the reproducibility of measured values.

In view of this point, it is an object of the present invention to provide a pattern edge detection method that can improve the reproducibility of measured values in a microdimensional measuring device.

[Means for Solving the Problems] A pattern edge detection method according to the present invention detects a pattern edge from a reflected light signal waveform or a secondary electron signal waveform obtained by irradiating a target pattern with a laser beam or an electron beam. In the pattern edge detection method,
The reflected light signal waveform or secondary electron signal waveform is compared with the reference signal waveform, and if the reflected light signal waveform or secondary electron signal waveform is dissimilar to the reference signal waveform, the focal position of the laser beam or electron beam is re-aligned. After the adjustment is made, pattern edges are detected again.

[Operation] If the reflected light signal waveform or secondary electronic signal waveform is dissimilar to the reference signal waveform, it is appropriate to treat these reflected light signal waveforms or secondary electronic signal waveforms as having low reliability. .

Here, in the present invention, when the reflected light signal waveform or the secondary electron signal waveform is dissimilar to the reference signal waveform, the focal position of the laser beam or electron beam is readjusted, and then the pattern edge is detected again. Therefore, pattern edge detection is never performed using a reflected light signal waveform or a secondary electronic signal waveform that is dissimilar to the reference signal waveform, that is, has low reliability, and is always similar to the reference signal waveform.
That is, pattern edges are detected using reliable reflected light signal waveforms or secondary electronic signal waveforms.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a block diagram showing essential parts of an example of a pattern edge detection device configured to carry out an embodiment of the present invention. It is constructed by providing a reference signal waveform reading means 2, a laser beam generation/scanning means 3, a focusing mechanism 4, a detector 5, an amplitude correction means 6, a signal waveform comparison means 7, and an edge detection signal output terminal 8. .

In this embodiment, first, a reference signal waveform SA corresponding to a pattern edge as shown in FIG. 2A is stored in the reference signal waveform storage means 1.

Next, after a laser beam is generated by the laser beam generation/scanning means 3, the focus of the laser beam is adjusted to a reference plane near the target pattern by the focusing device 14, and then a preset focus offset is performed. , scan the target pattern.

In this way, the detector 5 detects 5, for example, the second
A reflected light signal waveform SB as shown in FIG. B can be obtained.

The amplitude of this reflected light signal waveform Sa is corrected by the amplitude correction means 6. This correction is for the purpose of determining the similarity between the reflected light signal waveform Sa and the reference signal waveform S^, and is based on the difference between the baseline level BLa and the peak value PB in the reflected light signal waveform S11. The intensity fin(n=1.2.3·
・) is performed by correcting. In this case, the following formula is used: Note that in the formula, PA is the peak value in the reference signal waveform S^, and BLA is also the baseline level.

As a result of the correction, in this example, a corrected signal waveform SR' as shown by the broken line in FIG. are compared to determine their similarity. This similarity judgment is performed using so-called convolution (Conv) for sample points set near the pattern edges.
It is carried out by the method. That is, the value C is calculated using the following formula, and this C is set as a preset reference value Ct&
This is done by comparing.

(Σ(Work.-Im-')"l"=C(2) In this case, as shown in FIG. 3, the baseline level is determined from the baseline level BLa and peak value PB' of the correction signal waveform SR'.・Detection level DL and DL at 5 to 30% of the distance between peaks, for example, 15% inside,
The points EL and ER where the rate of change of the correction signal waveform SB' is maximum within the area between these detection levels DL and DL2 are regarded as pattern edges, and the left and right sides of the points EL and ER are 0.05 to 0.30 u rn. range, e.g. 0.1
0.01 to 0.10 μm intervals in the range of 0.08 m, for example,
It is preferable to set sample points at intervals of 0.02 μm.

Here, if C is C<(, am, the reflected light signal waveform Sa
It can be considered that reliability is high, and conversely, when C≧C1Il, reliability is low. Therefore, the signal waveform comparing means 7 outputs a predetermined pattern edge detection signal S0 to the pattern edge detection signal output terminal 8 when C□, and when C≧C1h, the reflected light signal waveform S6 is configured to reject this information and feed back this information to the focusing mechanism 4.

In addition, in response to this, the focusing mechanism 4 readjusts the focal position of the laser beam, and the laser beam generating/scanning means 3 rescans the target pattern using the readjusted focal position. The configuration is such that this operation is repeated until <Cah.

In this way, in this embodiment, the reflected light signal waveform SB
is amplitude corrected to obtain a correction signal waveform 88', and this correction signal waveform Si' is compared with the reference signal waveform S^. If this correction signal waveform Ss' is dissimilar to the reference signal waveform SA, the laser beam Since re-scanning and re-detection are performed by changing the focal position of
That is, pattern edges are never detected using the reflected light signal waveform SR with low reliability, and pattern edges are always detected using the reflected light signal waveform Sa that is similar to the reference signal waveform S^, that is, highly reliable. It will be done.

Therefore, by using the fifth embodiment, it is possible to improve the reproducibility of measured values in a micro-dimensional measuring device.

In addition, in the above embodiment, when the focus position is adjusted, if the focus position moves beyond a preset tolerance value, the focus position may be rejected as an error and an alarm may sound. can.

Further, in the case of C≧C1b, the device may be temporarily stopped and an alarm may be generated to request assistance from the operator.

Furthermore, the method of the present invention can also be applied to dry etching equipment.

That is, in the dry etching apparatus, the end point of etching is detected from the temporal change in the plasma emission intensity of a constant wavelength. Here, if an abnormality occurs in the apparatus, the waveform indicating the temporal change in plasma emission intensity will be different from that in a normal case. However, in conventional dry etching equipment, a threshold value is set for the plasma emission intensity and only the time required to reach this value is monitored. Therefore, even if the waveform indicating the time change in plasma emission intensity changes, if the time to reach the threshold value is the same as in normal times, it is determined that etching is being performed normally, and the device It was difficult to detect abnormalities early.

For example, FIG. 4 shows the temporal change in the plasma emission intensity, where X is a waveform showing the temporal change in the plasma emission intensity under normal conditions, and 1tl+ is a threshold value. Here, when the plasma emission intensity shows a time change like waveform X,
It is determined that the etching end point has been reached at time tAC. Further, when the plasma emission intensity shows a time change like waveform Y, it is determined that the etching end point has been reached at time tel, and in this case, an abnormality is notified.

However, when the plasma emission intensity shows a temporal change like waveform 2, this waveform Z also crosses the threshold value 1tk at time tAC. Therefore, in this case, even though it is thought that there is an abnormality, this is not reported.

Therefore, even in such dry etching equipment, by storing a normal reference waveform in the storage means and comparing this reference waveform with the waveform of the measured plasma emission intensity, it is possible to know at an early stage that there is an abnormality in the equipment. becomes possible.

[Effects of the Invention] According to the present invention, the reflected light signal waveform or the secondary electron signal waveform is compared with the reference signal waveform, and if they are dissimilar, the focal position of the laser beam or electron beam is readjusted and detected again. Therefore, pattern edge detection is never performed using a reflected light signal waveform or a secondary electronic signal waveform that is dissimilar to the reference signal waveform, that is, unreliable, and is always similar to the reference signal waveform. That is, pattern edges are detected using reliable reflected light signal waveforms or secondary electronic signal waveforms. Therefore, there is an effect that the reproducibility of measured values can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a pattern edge detection device configured to implement an embodiment of the present invention;
FIGS. 2 and 3 are diagrams showing signal waveforms, respectively, and FIG. 4 is a diagram showing temporal changes in plasma emission intensity. S^... Reference signal waveform S8... Reflected light signal waveform s, l... Correction signal waveform

Claims (1)

[Scope of Claim] A pattern edge detection method for detecting a pattern edge from a reflected light signal waveform or a secondary electron signal waveform obtained by irradiating a target pattern with a laser beam or an electron beam, Compare the secondary electron signal waveform with the reference signal waveform, and if the reflected light signal waveform or the secondary electron signal waveform is dissimilar to the reference signal waveform, readjust the focal position of the laser beam or electron beam. , and then detecting pattern edges again.