JPH01128338A - Surface observer - Google Patents

Abstract

PURPOSE:To make a clear-cut image displayable at high speed by setting up a bit mask circuit, nullifying a bit inclusive of noise, in secondary electron data collector part, and installing a color lookup table circuit, capable of selecting optional several colors, in an image display part. CONSTITUTION:Prior to starting a data collection, a main control part 1 specifies a gain of a gain control part 15. A beam 5 is subjected to test scanning and, after gain setting is over, whether what degree of a noise component is in secondary electron data is checked. Next, the main control part 1 indicates a bit mask circuit 18 that how many subordinate bits should be nullified. With this indication, the bit mask circuit 18 removes the specified noise component. In addition, a color lookup table 27 specifies a display color corresponding to intensity of a secondary electron. When it wants to emphasize an optional part, this case will be done by rewriting of the color lookup table. With this constitution, the optional part on a sample can be emphasized and displayed by only collecting the secondary electron intensity data discharged out of the sample one time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sample surface wt detection apparatus that scans a charged particle beam to remove irregularities and steps on a semiconductor substrate.

[Conventional technology]

Recently, for the production, failure analysis, and performance measurement of VLSI devices, ion implantation and processing at arbitrary positions on semiconductor substrates, and measurement of secondary electrons and backscattered electrons by electron beam irradiation at arbitrary positions have been developed. High precision is required. For this purpose, the charged beam is scanned and irradiated onto the desired specific area.

A technique is essential for observing the surface of a semiconductor substrate by measuring the intensity of the secondary electrons emitted from the irradiation part, and for performing correspondence and alignment with the actual semiconductor substrate with high precision.

FIG. 2 is a basic configuration diagram of a conventional sample surface W4 detection device. The charged particles here are ions. The main body of this device is Monthly Semiconductor World.

As discussed in the November 1983 issue, pages 52 to 57, ions extracted from the ion source 3 are focused by an electrostatic lens 4 to form an ion microbeam (hereinafter referred to as beam) 5. The sample 6 is irradiated with the laser beam. Here, 1 is a main control unit that controls the entire sample surface observation apparatus, and 2 is an internal bus. In response to instructions from the main controller 2, the deflection controller 10 generates a deflection signal 11 to the deflector 7, and scans the beam 5 over the sample 6. Secondary electrons e are emitted from the sample 6 by the irradiation with the beam 5 and are detected by the secondary electron detector 8. Note that 9 indicated by a broken line is a vacuum container. The secondary electronic data collection section 13 includes a data collection control section 14. Gain control section 15, A/D conversion section 16. It is composed of a buffer memory 17.

Before starting data collection, the main control section 1 specifies the gain of the gain control section 15. The gain control unit 15 converts the intensity 21 of the secondary electrons into secondary electron analog data 22 having an arbitrary amplitude. Data collection is performed according to the timing of the deflection synchronization signal 12 from the deflection control section 10, and the data collection control section 14 sends the data collection signal 1 to the A/D conversion section 16.
9, converts the secondary electron analog data 22 into secondary electron digital data (hereinafter referred to as secondary electron data) 23, and stores the secondary electron data 23 in the buffer memory 17 at the timing of the data storage signal 20. do.

The image display section 24 has a graphic memory 25. Graphic control unit 26. Color lookup table (CL
(abbreviated as T) 27 and CRT interface 28. CR
Consists of T29. After data collection is completed, the main control unit 1 transfers the secondary electronic data 23 stored in the buffer memory 17 to the graphic memory 25. Graphic control section 2
6 is secondary electronic data 23' in the graphic memory 25
is read out and the secondary electronic data 23' is given to the CLT 27. The CLT 27 provides an RGB signal 30 to the CRT interface 28 in response to the secondary electronic data 23'. The CRT interface 28 supplies RGB signals 30' to the CRT 29, and an image of the sample surface can be displayed on the CRT 29.

Next, the color lookup table (hereinafter abbreviated as CLT) will be explained in detail. The configuration of the CLT is shown in FIG. 35 is the CLT array, and the secondary electron data 23 is CLT.
Matches the address of the LT array. The color displayed on the CRT is determined by three values: red, R, green, and blue. 32, 33
．． 34 are the values of red R, green G, and blue B, respectively. If the number of bits in each array is m, 25+m colors can be created. If the size of the array is 2n, the number of colors that can be displayed per degree is 2n. Here, secondary electronic data 23
When the number of bits is n, the secondary electronic data 23 is displayed on the CRT in 2'' gradation color.

Conventional image display units do not have CLTs, or even if they do have CLTs, the contents of the CLTs are fixed.

An example of the color allocation of conventional CLT is shown in FIG. For a single color, only 2n gradations from dark to light were assigned.

Next, a procedure for displaying a secondary electron image will be described. The image of the surface of the sample is C
The gain of the gain control section 15 is set for display on RT. First, the surface of the sample is test scanned, and the gain control unit 15 is set so that the maximum value of the secondary electron data 23 becomes 80% to 90% of the upper limit of the range in which the secondary electron data 23 can be obtained.
Set.

Since colors are assigned to CLT as shown in Figure 4,
With the gain setting method described above, areas with large steps and unevenness are emphasized and clearly visible, but areas with small steps and unevenness lack clear image contrast and are difficult to discern. Therefore, if you want to clearly see a part with a small step, that is, a part with weak contrast, the value of the secondary electron data 23 of the part with a small step should be 80% to 90% of the upper limit of the range that the secondary electron data 23 can take. The gain control section 15 had to be set again.

[Problem that the invention seeks to solve]

However, in the sample surface observation device described above, the gain setting value is changed depending on the condition of the sample surface.

The surface of the sample must be scanned each time.

As a result, the surface of the sample was contaminated, or the surface of the sample was charged up, making it impossible to see images of secondary electron data. Furthermore, when displaying a 1024 x 1024 dot screen, it takes about 5 seconds even if scanning is performed at a very high speed of 5 μs per point, and considering the data transfer time between the buffer memory 17 and the graphic memory 25, There was a problem that it took several seconds for the screen to be displayed, and the waiting time increased when scanning was performed many times.

[Means for solving problems]

An object of the present invention is to provide a sample surface observation device that eliminates the above-mentioned disadvantages of the prior art and can display high-contrast images at high speed even on small steps, uneven parts, and gentle slopes on the sample. There is a particular thing.

In order to achieve the above object, the present invention scans and irradiates a sample with a charged beam obtained by focusing charged particles extracted from a charged particle source, and detects secondary electrons emitted from the sample. In an apparatus that observes the surface of a sample from the intensity of secondary electrons, a bit mask circuit for disabling bits containing noise is placed after the A/D conversion circuit of the secondary electron data collection section, and the image display section We adopted a configuration that includes a color look-up table circuit that allows you to select any number of colors to display on the screen.

[Effect]

The color lookup table specifies display colors in accordance with the intensity of secondary electrons. If you want to emphasize any part, you can do so simply by rewriting the color lookup table. Further, the bit mask circuit removes noise components. This prevents noise components from being emphasized and displayed when emphasizing small irregularities or steps on the sample surface, that is, when emphasizing the lower bits of secondary electron data.

Due to this effect, when displaying an arbitrary part of the surface of the sample with emphasis, the present invention rescans the load beam by changing the gain of the gain control section connected to the secondary electron detector, and displays the secondary electrons. There is no need to collect data many times, and contamination and charge-up on the sample surface can be minimized. Additionally, any part can be highlighted at high speed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Here, the charged particles are assumed to be ions. 1 is a main control unit that controls the entire sample surface inspection device, and 2 is an internal bus. The ion source 3 is a high-brightness liquid metal ion source, and ions extracted therefrom are focused by an electrostatic lens 4, and a beam 5 thereof is irradiated onto a sample 6. In the sample surface wt detection device, a blanking electrode is provided in the middle of the ion optical system for beam on/off control, but it is omitted in FIG.

In response to instructions from the main controller 1, the deflection controller 10 controls the deflector 7.
A deflection signal 11 is generated for the sample 6, and the beam 5 is scanned onto the sample 6. By irradiating the beam 5, secondary electrons e are emitted from the sample and detected by the secondary electron detector 8. here,
9 is a vacuum container.

The secondary electronic data collection section 13 includes a data collection control section 14.
Gain control section 15. A/D converter 16° bit mask circuit 18. It is composed of a buffer memory 17. Before starting data collection, the main control section 1 specifies the gain of the gain control section 15. The gain control unit 15 controls the intensity 21 of secondary electrons.
is converted into secondary electron analog data 22 having an arbitrary amplitude.

After performing a test scan with the beam 5 and completing the gain setting, it is determined how much noise component there is in the secondary electron data. The main control unit 1 instructs the bit mask circuit 18 how many lower bits are to be invalidated.

Here, a configuration diagram of the bit mask circuit 18 is shown in FIG. 5 and explained. The bit mask circuit 18 is composed of a bit mask register 36 and an AND circuit 37. Here, the bus width of the internal bus 2 is 16 bits. The main control unit 1 sets data in the bit mask register 36. It is assumed that data in bits set to 1 is valid, and data in bits set to 0 is invalid. The number of bits of the secondary electron data 23 is set to n bits. However, n(16
shall be. Now, assuming that the lower 1 bit of the secondary electron data 23 contains a noise component, the bit mask register 3
6 should be set to FFFE in hexadecimal. The lower one bit of the secondary electronic data 31, which is the output of the bit mask circuit, is invalid, that is, zero.

Returning to the explanation of FIG. 1 again. Data collection is performed according to the timing of the deflection synchronization signal 12 from the deflection control section 10, and the data collection control section 14.

A data collection signal 19 is generated in the A/D converter 16 to convert the secondary electronic analog data 22 into secondary electronic data 23. Secondary electronic data 31, which is the output of the bit mask circuit 18, is stored in the buffer memory 17 at the timing of the data storage signal 20.

The image display section 24 has a graphic memory 25. Graphic control unit 26. CLT27. CRT interface 28
．． It is composed of CRT29. After data collection is completed, the main control unit 1 transfers the secondary electronic data 31 stored in the buffer memory 17 to the graphic memory 25. The graphic control unit 26 reads out the secondary electronic data 31' in the graphic memory 25 and inputs the secondary electronic data 3 to the CLT 27.
1' is given. The CLT 27 provides an RGB signal 30 to the CRT interface 28 in accordance with the secondary electronic data 31'. CRT interface 28 provides RGB signals 30' to CRT 29.

An image of the sample surface is displayed on the CRT 29.

An example of specifying a color lookup table when displaying an image for the first time is shown in FIG. 6(a). Secondary electronic data 31
Assume that the lower 1 bit is invalid. In this case, there is no odd-valued secondary electron data 31, so the odd-numbered addresses of the color lookup table are not used. The display color is set to be the darkest when the value of the secondary electronic data 31 is O, and the darkest when it is 2" -2, and to have a linear color gradation between them. By doing this, unevenness and steps are displayed. The large part of is emphasized.

Next, FIG. 6(b) shows an example of emphasizing portions with small irregularities and steps. Consider a case where secondary electron data 31 emphasizes data smaller than 2". However, O< i <
It is n. Here, as in (a), secondary electron data 3
Assume that the lower 1 bit of 1 is invalid. First, all secondary electron data 31 values larger than 2''-2 are displayed in the same color.
When the range is n-t-2, the color lookup table is specified so that the displayed color has linear gradation.

FIG. 6(C) shows a second example of emphasizing areas with small unevenness or steps, that is, areas with weak contrast. Here, as in (a), the lower 1 bit of the secondary electronic data 31 is invalid. Suppose there is. A color lookup table is specified so that every other piece of secondary electronic data 31 is displayed in the same color.

Here, the colors are specified to be white, black, white, and black in descending order. When such a color lookup table is specified, a secondary electron image of stripes of two colors, white 39 and black 40, as shown in FIG. 7 is created. The fringes act in the same way as contour lines, and the spacing between the fringes reveals minute inclinations and steps on the sample surface.

Furthermore, it is also possible to add gradations of color density to the stripes.

Next, specific numerical examples will be given regarding the display time of the secondary electron image. A Ga liquid metal ion source was used as the ion source, the ion microbeam was a 16 K e VGa+ beam, the beam diameter was 0.5 μm, and the current density was 0.3 A/c.
It is d. The data displayed on the 1024 x 1024 dot screen is 1 mega point.

If the beam irradiation time per point is 5 μS, it takes 5 seconds to irradiate 1 mega point. Furthermore, considering the data transfer time between the buffer memo IJ 17 and the graphic memory 25, it takes several seconds to display one screen.

After this, if you want to emphasize any part of the screen, you only need to rewrite the color lookup table, so it was found that this can be done in less than 1 second.

In the above embodiments, the charged particles irradiating the sample were ions, but it was found that similar effects could be obtained when the charged particles were electrons.

〔Effect of the invention〕

As explained above, according to the present invention, the sample surface IjI
By simply collecting the intensity data of the secondary electrons emitted from the sample once by scanning the charged beam in the detection device,
Any part on the sample can be highlighted and displayed. As a result,
Contamination and charge-up on the sample surface can be minimized. Furthermore, the time required to increase the intensity of any part of the secondary electron intensity on the sample can be shortened, making it possible to increase efficiency.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the overall configuration of an embodiment of the present invention, Figure 2 is a block diagram showing the overall configuration of a conventional device, and Figure 3 is a block diagram showing the overall configuration of a conventional device.
The figure is an explanatory diagram of a lookup table, Part 4 and Figure 6 are explanatory diagrams showing an example of specifying data in a lookup table, Figure 5 is a configuration diagram of a bit mask circuit, and Figure 7 is a detailed explanation of the present invention. This is a secondary electron image to explain. DESCRIPTION OF SYMBOLS 1... Main control part, 2... Internal bus, 3... Ion source, 4... Electrostatic lens, 5... Ion microbeam, 6... Sample, 7... Deflector , 8... Secondary electron detector, 9... Vacuum container, 10... Deflection control unit, 1
3... Secondary electron data collection section, 14... Data collection control section, 15... Gain control section, 16... A/D conversion section, 17... Buffer memory, 18... Bit Mask circuit, 24... Image display unit, 25... Graphic memory, 16... Graphic control unit, 27...
- Color lookup table, 28-CRT interface, 29 - CRT. 32...Red data, 33...Green data, 34.
...Blue data, 35...Color lookup table array, 36...Bit mask register, 37...
AND gate, 38...Secondary electron image, 39...White area. Kaya 1 Figure Well 2 Figure Kaya 3 Figure Kaya 4 Figure Seri 5

Claims (1)

[Claims] 1. A deflection control unit that scans a charged beam in which charged particles extracted from a charged particle source are focused and irradiates the surface of a sample;
A secondary electron data collection unit that detects secondary electrons emitted from the sample by irradiation with charged particles, converts the intensity of the secondary electrons into digital values, and displays the secondary electron data on the screen. In a sample surface observation device consisting of an image display section and an image display section, a bit mask circuit for disabling bits containing noise components is placed after the A/D conversion circuit of the secondary electron data acquisition section, and a screen 1. A surface observation device comprising a color look-up table circuit capable of selecting an arbitrary number of display colors from a plurality of colors. 2. In the method of displaying the collected secondary electron data on the display screen of the image display section using the bit mask circuit and the color lookup table circuit, depending on the size of the secondary electron data collected on the display screen, A first mode in which gradation is displayed linearly, and a second mode in which a specific numerical range of the collected data is emphasized and displayed by masking specific multiple bits of the collected secondary electron data. 2. The surface observation device according to claim 1, further comprising a display step of selecting one of the following.