JPH01201109A - Electron beam length measuring machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electron beam subdirector.

(Prior Art) With rapid progress in microfabrication technology, integrated circuits are becoming increasingly finer. The dimensions of the circuit elements have been miniaturized from several microns to one micron. Since the dimensions of the element are important factors in determining the basic performance of electronic circuits such as amplification and frequency characteristics, accurately measuring the pattern width within the chip (material) is essential in designing integrated circuits. It becomes necessary.

An electron beam length measuring machine is a device that accurately measures the pattern width within a material, and an example of its configuration is shown in FIG.

The electron beam Bi emitted from the electron beam gun 1 is turned on and off by a blanking electrode 2 and then converged by a converging lens 3. The focused electron beam 3i is deflected in two-dimensional directions while passing through the first scanning system 4 and the second scanning system 5. This deflection control is performed according to instructions from CPtJll. The deflected electron beam 3i is converged by the objective lens 6 and falls onto the material table 7 with lI! placed material 8
Focus on the top. In other words, the material 8 is irradiated with the electron beam 3i.

As the electron beam 3i scans over the material 8, reflected electrons or secondary electrons are generated from the beam irradiation point of the material 8. Here, the direction in which the material 8 is scanned is digital scanning in which the electron beam 3i is run intermittently at regular intervals. The m-separate interval (scale unit) is, for example, 1/100 of the scanning distance of the t-beam Bi.
It is set to about 0. For example, to measure a line width of 1 micron, scan the electron beam [3i] by a width of 3 microns and set the 111th position on the scale to 0.003 micron.

The intensity of reflected electrons or secondary electrons generated from the material surface varies depending on the material of the irradiation point. Therefore, a detector 9 placed above the material surface detects these electrons, and the electrons are amplified by an amplifier 10 and fed to a cpuil.

The CPU 11 determines the pattern width as a sub-length based on the signal detected by the detector 9. Note that the scanning distance and the middle of the scale are precisely calibrated using a reference pattern created by an electron beam lithography device. In actual length measurements, digital scanning is usually performed using a D/A converter with a resolution of 1024 steps (10 bits) or 2048 steps (11 steps) in order to improve the reproducibility and accuracy of length measurements. . When the beam scanning for one field is completed, the driving machine groove 12 is created and the material stage 7 is moved in accordance with a command from the CPIJll.

Reference numeral 13 denotes a frame for storing pattern information on the entire surface of the material 8. Before measuring the line width, the entire surface of the material 8 is scanned, and the reflected signal is sent to the CPU 11 built-in A/
The data converted into digital data by a D9 converter (not shown) is stored in the frame memory 13. The contents of the frame memory 13 are stored in the CR as necessary.
It can be displayed on T14.

By the way, in order to measure the line width of a pattern on a material, the material is scanned with an electron beam (intermittent digital scan), and the line width is measured using a mark detection method from secondary electron signals and reflected electron signals. do. Figure 3 shows the basics of line width measurement using the mark detection method! It is an explanatory diagram. As shown in the figure, the pattern 20 on the material 8 is scanned with an electron beam Bi, the secondary electron signal generated at that time is detected, and when its peak is captured, a detection signal as shown in the figure is obtained. This detection signal has a waveform 19 having a peak at the edge of the pattern 20, and by measuring between these peaks using a threshold method or the like from this waveform, the line width can be obtained.

(Problem to be solved by the invention) The capacity of the frame memory 13 is 512×5 pixels.
12 is the standard. The higher the number of pixels in the frame memory 13, the better the resolution, but such a frame memory with a high number of pixels is much more expensive than one with 512x512 pixels. Moreover, such a frame system with a high number of pixels is limited by element speed, and it takes a long time to read one frame image. Therefore, when line scanning a length measurement point in length measurement mode, it is limited by the number of pixels of this frame memory (512 points per line).
Measurement with high resolution and tS accuracy becomes impossible.

The present invention has been made in view of these points, and
The purpose is to realize an electron beam length measuring machine that can perform i-accuracy line width measurement without increasing the capacity of the frame memory.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, is capable of storing a signal generated by 1q from a material when an electron beam is irradiated on the material in a frame memory as image data, and when measuring a length, In an electron beam length measuring machine that scans one line of a specific pattern and measures the width of the pattern, the signal sampling speed during length measurement is several times the signal sampling speed when storing the signal in the frame memory. It is characterized by being fast.

(Function) In the present invention, for example, a relatively inexpensive 512x51
When using a frame memory with a pixel count of 2, in actual length measurement mode, for example, 2048 points of data, which is 4 times as much, is acquired per line and compared when monitoring the image, allowing highly accurate length measurement. It is based on configuring. In this case, if the number of points 1 to 4 is increased by 4, the scanning speed of the electron beam will be the same during image monitoring to supply the signal q to the frame memory and during length measurement to supply the signal to the length measuring unit. Conditions such as charge-up on the material differ depending on the length measurement and length measurement, which is not desirable. Therefore, in the present invention, the sampling speed during length measurement is compared with the sampling speed during monitoring, and the sampling speed is increased according to the difference in the number of sampling points. For example, 512X51
When images are monitored using frame memory No. 2 and length measurement is performed at 2048 points, the scanning speed of the electron beam during length measurement is increased four times.

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

FIG. 1 is a block diagram of main parts showing an embodiment of the present invention.

Components that are the same as those in FIG. 2 are designated by the same reference numerals. In the figure, reference numeral 31 denotes a deflector that deflects the electron beam 3i in two-dimensional directions, and corresponds to the first scanning system 4 and the second scanning system 5 in FIG. Reference numeral 32 denotes a deflection unit that outputs a signal giving a scanning width to the deflector 31, and receives a command to start scanning and data regarding the width of the scanning area and the like from the CPU 11. 33
is a length measuring unit that receives the output of the detector 9 and measures the line width of a pattern using a mark detection method.

4 is a clock generator that generates an original clock for operating the system; 35 is a first sampling device that receives the output clock (1 μs cycle) of the clock generator 34 and generates a sampling clock for writing data to the frame memory 13; A clock generator 36 is a second sampling clock generator that receives the output clock (0.25 μs period) of the clock generator 34 and generates a sampling clock for length measurement. Note that the deflection unit 32 is supplied with an output clock (0.25 μs cycle) from a clock generator 34 .

From the above, the sampling rate for the length measuring unit 33 is 1
This results in a numbering speed four times faster than the numbering speed for the frame memory 13 per line scan. The output of the clock generator 34 is given to the CPU 11 as a machine clock, and to the deflection unit 32 as a synchronous clock. The operation of the device configured as described above will be explained as follows.

An electron beam B1 emitted from an electron gun (not shown) is deflected by a deflector 31, and scans an area on the material 8 corresponding to each magnification. The area settings at this time are CPU1
The deflection unit 32 that received the instruction No. 1 performs this. At this time, the secondary signal (backscattered electrons) obtained from the material 8 is transmitted to the detector (M
CP)9. The detected signal is converted into digital data using a sampling clock by a Δ/D converter (not shown) built in the frame memory, and then stored in the frame memory 13 or the length measuring unit 33. During length measurement, the electron beam is line-scanned at a target location of a target pattern, and a signal based on this line scan is taken into the length-measuring unit 33. On the other hand, when monitoring the image, the electron beam is
The material 8 is scanned dimensionally, and scan line data covering the entire surface of the material 8 is sequentially stored in the frame memory 13. The image data stored in the frame memory 13 is read out by the CPU 11 as necessary, and
14.

Now, the second sampling clock generator 36 generates a sampling clock that is four times faster than the output clock of the first sampling clock generator 35. Therefore, when one piece of data is stored in the frame memory 13 during monitoring, four pieces of data are stored in the length measuring unit 33 during length measurement. In other words, it has four times the resolution.

Specifically, when one line of 512 pieces of data is stored in the frame memory 13, the length measurement unit 33 stores 2048 pieces of data, which is four times that number.

The length measuring unit 33 measures the line width using the waveform of the measurement line based on the obtained data. Therefore, the length measuring unit 33 can measure the line width with four times the accuracy when determining the line width from the data stored in the frame memory 13. At this time, the time for one line scan is 1 μ5 x 512 = 512 (μS) for both data storage in the frame memory 13 and length measurement.

0.25×2048=512 (μS>).

Moreover, these clock sources (clock generator 3
Since the clock from 4) is used as the sampling clock, synchronization is achieved. Therefore, when monitoring and measuring length, there is a charge-up of the material! 1 becomes equal.

In the above description, sampling clocks of 1 μs and 0.25 μs were used, respectively, but the present invention is not limited to this, and clocks with different periods can be used as sampling clocks. Also, the ratio of the clock cycle when reading the frame memory to the clock cycle when 1 line or 111 length is not limited to 4:1,
May be optional.

Furthermore, the deflection unit always keeps the electron beam at 0.25μ.
The scanning speed of the electron beam may be set to 1 μs during monitoring and 0.25 μs during length measurement.

(Effects of the Invention) As described above in detail, according to the present invention, by performing line width sub-length for one line scan at a sampling speed several times faster than when writing image data to the frame memory, Accordingly, it is possible to realize an electron beam length measuring machine that can perform highly accurate line width measurement without increasing the number of products.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the main part of an embodiment of the present invention, Fig. 2 is a diagram showing an example of the configuration of an electron beam length measuring machine, and Fig. 3 is a diagram explaining the principle of line width length measurement using the mark detection method. It is. 8...Material 9...Detector 11...C
PIJ 13...Frame memory 14...
CRT 31...Deflector 32...Deflection unit 33...Length measurement unit 34...Clock generator 35. 36...Sampling clock generator Patent applicant Nihon Denshi Co., Ltd. Patent Attorney I
Shimafuji Jigai 1 person

Claims (1)

[Claims] When an electron beam is irradiated onto a material, the signal obtained from the material can be stored in the frame memory as image data, and when measuring the length, the electron beam scans a specific pattern on the material one line and measures the width of the pattern. An electron beam length measuring machine characterized in that the sampling speed of a signal during length measurement is several times faster than the sampling speed of a signal when storing the signal in the frame memory.