JPH0375046B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic pattern length measurement method using charged particle beam scanning.

[Prior Art] In recent years, integration has progressed from ICs to LSIs and super LSIs, and patterns have become smaller along with this. Due to the miniaturization of patterns, methods that use electron beams, which have higher resolution than those that use light, are attracting attention as methods for measuring the width of patterns.

Now, the method of using this electron beam is to scan the electron beam over a pattern and observe the reflected electron image, secondary electron image, etc. The mainstream method is a cursor method in which, for example, two cursors are displayed, the operator moves each cursor to a width measurement position of a pattern image displayed on the screen, and measures the dimension between the two cursors.

[Problems to be Solved by the Invention] However, with this method, the operator must use his/her nerves to move the cursor to the measurement location each time the measurement location changes, which is not only cumbersome to operate; , automatic high-speed measurement is not possible.

The present invention is aimed at solving such problems.

[Means for Solving the Problems] Therefore, the pattern length measurement method of the present invention scans a pattern with a charged particle beam, and detects reflected electrons or secondary electrons generated from the pattern by this scanning. Find the coordinates corresponding to multiple ends of the pattern, find the difference between each of the found coordinates, compare these found differences with a preset expected value, pick out the length that is close to the expected value, and calculate this. The target length measurement value is automatically obtained based on the extracted difference.

[Operation] Generally speaking, when looking at a chip or the like on which a large number of patterns are drawn, there are cases in which the chips are a collection of patterns all having the same size, or a group of patterns having several different sizes. In any case, chips and the like form a group of patterns having the same size.
A large number of these chips are then created. The approximate dimensions of these patterns can be determined by measuring the patterns of the same chip in advance using a pattern length measurement method using the cursor method, which displays two cursors on the cathode ray tube. There used to be. Therefore, this known value is stored in advance as a predicted value. On the other hand, the pattern is scanned with a charged particle beam, and multiple end coordinates of the pattern are determined based on detection signals obtained with this scanning. The difference between the determined coordinates is determined. If the obtained plurality of differences are compared with the predicted values, there should be some among these differences that are extremely close to the predicted values. Therefore, it is possible to extract a difference that is extremely close to the expected value, and obtain the desired length measurement value based on this extracted difference.

[Example] FIG. 1 shows an example of an apparatus implementing the pattern length measurement method of the present invention. In the figure, 1 is an electron gun, and an electron beam emitted from this electron gun is focused by a focusing lens 2 onto a material 3 on which a pattern has been drawn in a previous step. Further, this electron beam is transmitted to a scanning signal generating circuit 5 operated by a command from a control device 4.
The material 3 is scanned by the deflector 6, which operates according to a scanning signal from the deflector 6. The reflected electrons generated on the material 3 by this scanning are detected by the reflected electron detector 7. The output of this detector is sent to the control device 4 via the amplifier 8, and at the same time, an output (scanning signal) synchronized with the output from the scanning signal generating circuit 5 to the deflector 6 is supplied. It is also sent to the cathode ray tube 9. This cathode ray tube is
By modulating the brightness, a single marker M can be placed at a position on the screen according to a command from the control device 4. Incidentally, the position of this marker M can also be controlled by external operation.

Now, as shown in FIG. 2, the control device 4 has previously calculated the expected dimension L ₀ plus the width α of only the hem S of the pattern to be measured (L ₀ + α) and subtracted (L ₀ − α) is set.

Then, in response to a command from the control device 4, the electron beam scans a predetermined position of the pattern on the material 3 to be measured, as shown in FIG. 3a. Backscattered electrons generated from the pattern by this scanning are detected by a backscattered electron detector 7 and sent to the control device 4 via an amplifier 8. Of the signals based on such reflected electrons (Fig. 3c), this control device
The negative level signal portion is inverted (Fig. 3 d), and the signal in Fig. 3 d reaches a preset level Le from a certain scanning time t ₀ (a, b, c, d).
Detect the time values (ta, tb, tc, td) until then. These time values are determined by the number of clock pulses generated from time t ₀ to times a, b, c, and d.
This control device uses these detected values ta, tb, tc, td
The difference between each other, namely (tb−ta), (tc−ta), (tc−
tb), (td−ta), (td−tb), and (td−tc).
Then, compare the difference between these detected values with the preset values (L ₀ + α) and (L ₀ - α), and find the value closest to (L ₀ + α) among these difference signals. (td.
−ta), the value (tc−tb) closest to (L ₀ −α) is extracted. The former is the width of the hem near the bottom B of the pattern, as shown in FIG. 3b, and the latter is the width of the hem near the top T of the pattern.

In the case of a resist pattern, the width dimension of the pattern is generally selected from the width dimension of the bottom part near the bottom part B. Therefore, in the above embodiment, the control device 4 selects the width dimension of the pattern ( _td −ta) as the pattern width dimension.

In addition, as mentioned above, if you measure the width of the hem near the bottom B of the pattern and the width of the hem near the top T, you can know the width of the hem. Since the formed metal pattern has a rectangular cross section (i.e., the width of the hem is small), the width of the hem near the top T is selected as the width of the pattern, so we measured it. The width dimension of the hem near the top T is then selected.

As shown in Figure 5a, pattern Pa and pattern
When measuring the width dimension of pattern Pa when Pb is spaced apart from the width dimension of pattern Pa,
When measured using the method described above, as shown in Figure 5b, from time t ₀ a, b, c, d, e, f, g, h
The mutual difference (tb−
ta), (tc−ta), (tc−tb), td−ta), ………, (
tf
−ta), (tf−tb), (tf−tc), ..., (tg−te),
(tg - tf) is compared with the preset expected value La of the width of the hem near the bottom, and the value closest to this expected value is taken, but originally (td - ta)
Where to take out, unrelated to pattern dimensions (tf
-tc) may be removed. Therefore, in such a case, for the peaks P ₁ and P ₃ obtained from the left edge of the pattern, the rising signals are
Peak P ₂ obtained from the right edge of the pattern,
For _P4 , input the waveform shape so that the falling signal is selected. By doing this, the width dimension (td-ta) of the hem near the bottom of the original pattern Pa is extracted from the mutual difference between the selected ta, td, te, and th.

In addition, there is also a length measurement method in which the width dimension is the value between the peaks of the signal from the backscattered electron detector, and a length measurement method in which the signal from the reflection detector is differentiated and the width dimension is determined between the inflection points. Inventions can be applied.

[Effects of the Invention] As shown in FIG. 4, the present invention does not require the operator to use his or her nerves to move the cursor to the measurement location, even if there is a pattern Pd of a different size in the vicinity of the pattern Pc to be measured. No more operation,
Automatic high-speed measurement is now possible.

[Brief explanation of drawings]

Fig. 1 shows an example of an apparatus implementing the pattern length measurement method of the present invention, Fig. 2 shows a cross-sectional view of the pattern, and Fig. 3 shows an example of a device implementing the pattern length measurement method of the present invention. FIG. 4 is for supplementary explanation of the effects of the present invention, and FIG. 5 is for supplementary explanation of other embodiments of the present invention. 1: Electron gun, 2: Focusing lens, 3: Material, 4:
Control device, 5: Scanning signal generation circuit, 6: Deflector,
7: Backscattered electron detector, 8: Amplifier, 9: Cathode ray tube.

Claims (1)

[Claims] 1. Scan the pattern with a charged particle beam, determine coordinates corresponding to multiple ends of the pattern based on reflected electrons or secondary electron detection signals generated from the pattern by this scanning, and calculate the distance between each of the determined coordinates. This method calculates the difference between the two lengths, compares the calculated difference with a preset expected value, extracts the length that is close to the expected value, and automatically obtains the desired length measurement value based on this extracted difference. Pattern length measurement method.