JPH04315756A - Signal processing system of scan type electron microscope using video bus - Google Patents

Abstract

PURPOSE:To prevent the band deterioration of signals and lowering of S/N ratio and also to simplify the constitution of a system by digitizing image data, and subjecting the data to signal processing through a video bus. CONSTITUTION:A detection signal amplified by a premain amplifier 21 or the like and detected by a secondary electron detector 11 or the like is converted into a digital signal by A/D converters 121-123 via buffers 111-113. The digital signal obtained is transferred through a video bus 130 and sampled into a CPU 131 and a DSP 132. The CPU 131 sets modes of processing (performed) at the DSP 132 and the DSP 132 performs image data processing in real time. In this case, addition of various kinds of processing functions is made possible by changing software. Image data are thus digitized and subjected to signal processing through the video bus and thereby the band deterioration of signals and lowering of S/N ratio can be prevented and also the constitution of the system can be simplified.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing system for a scanning electron microscope that uses a video bus to digitally process detection signals in a scanning electron microscope.

0002

2. Description of the Related Art FIG. 2 is a diagram showing a signal processing system of a conventional scanning electron microscope.

In the figure, 11 is a secondary electron detector, 12 is a backscattered electron detector, and 13 is an EMF (Electro Moti
ve Force) detector, and 14 is an AEI (Absor
tion Electric Image) detector, 15 is an infrared detector, 21 to 25 are preamplifiers, 26
is a cable, 31 to 35 are amplifiers, 40 is a selector, 4
1 to 45 are buffers, 46 is a selection switch, 47 is a cable, 50 is an image signal processing circuit, 51 is an automatic contrast/brightness adjustment circuit, 51a is a hold circuit, 51b is a gain adjustment circuit, 52 is an automatic focus circuit, and 53 is a 54 is a CPU, 55 is a lens system, 56 is an FIS (frame integration system), 60 and 61 are switches, 62 is a first display, 63 is a recording display, and 64 is a second display.

An electron beam is irradiated onto a sample (not shown) through a lens system 55, and an image of the sample is detected by each detector. The secondary electron image is detected by the detector 11 and taken out through the preamplifier 21, cable 26, and amplifier 31. The backscattered electron images are detected by two detectors 12a and 12b provided on the left and right, respectively, and taken out through preamplifiers 22a and 22b and multistage amplifiers 32a and 32b. An EMF image, that is, an image signal obtained when an electron beam is irradiated onto an IC pattern, is detected by an EMF detector 13 and extracted through a preamplifier 23 and an amplifier 33. The electron absorption image is detected by the AEI detector 14, and the preamplifier 24
, an amplifier 34. The infrared image is detected by an infrared detector 15 and extracted through a preamplifier 25 and an amplifier 35. If necessary, the desired image signal is further detected by another detector. These detected image signals are selected by a selector 40 having buffers 41 to 45 and a selection switch 46, and sent to an image signal processing circuit 50 through a cable 47 as a single or multiple superimposed signals.
transmitted to.

The image signal processing circuit 50 includes an automatic contrast/brightness adjustment circuit 51, an automatic focus circuit 52, and an automatic astigmatism correction circuit 53, each of which is controlled by a CPU 54 to set conditions. In the automatic contrast/brightness adjustment circuit 51, a hold circuit 51a detects and holds amplitude values such as an average value and a maximum value, and a gain adjustment circuit 51b adjusts the gain based on these values. Also, CPU
The lens system 55 is controlled by the autofocus circuit 52 and the autostigmatism correction circuit 53 whose conditions are set according to the above conditions, so that a desired image signal can be obtained.

The detected image signal is subjected to frame integration by the FIS 56 to reduce noise and perform image processing such as edge enhancement. Then, when the switches 60 and 61 select a signal directly from the cable 47 or a signal after contrast/brightness adjustment, the first display 62 displays the original image signal as it is when scanning the sample surface. In order to improve the S/N ratio, the signal at this time is
For example, it takes several tens of seconds or even 100 seconds to form one screen, so the human eye sees only lines rather than images. In addition, the FIS 56 performs image processing such as edge enhancement and screen division, and once the data is stored in memory, it is read out at TV rate and displayed on the second display 64 as an image that can be recognized by the human eye. . Further, the image signal from the FIS 56 is selected by the switch 61, displayed on the recording display 63, and photographed.

[0007]

[Problems to be Solved by the Invention] In the conventional signal processing system shown in FIG. 2, image signals are transmitted as analog signals. While leading to the display, there was a problem that the band deteriorated to 5 to 6 MHz depending on the number of stages, and noise was added due to the multi-stage amplification stage, resulting in a decrease in the S/N ratio. Further, because of analog processing, contrast, brightness adjustment, focusing, astigmatism correction, etc. must be processed by separate dedicated circuits, making the system configuration complicated.

The present invention is aimed at solving the above problems, and provides a scanning electron microscope using a video bus that can prevent signal band deterioration and S/N ratio deterioration and simplify the system configuration. The purpose is to provide a signal processing system for

[0009]

[Means for Solving the Problems] A signal processing system for a scanning electron microscope using a video bus of the present invention irradiates a sample with an electron beam and detects sample information with one or more detectors,
A scanning electron microscope that processes and displays detected signals includes an A/D converter that converts the detected analog signal into a digital signal, a video bus that transmits the A/D converted image data, and a video bus that transmits the A/D converted image data. a digital signal processing circuit that processes image data input through a bus; a CPU that controls the digital signal processing circuit through a control bus;
It is characterized by comprising a video bus that transmits output data of a digital signal processing circuit, and a D/A converter that converts the processed data transmitted through the video bus into an analog signal.

0010

[Operation] The present invention digitizes a sample image signal obtained by scanning a sample surface, transmits a large amount of image data at high speed through a video bus, and processes the image in real time by a digital signal processing circuit controlled by a CPU. By D/A converting the processed data, the analog amplification stage is limited to the input and output stages to prevent band deterioration and S/N ratio deterioration, and various software for digital signal processing is available. This makes it possible to perform various types of image processing with a single digital signal processing circuit and simplify the system configuration.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention,
The same numbers as in FIG. 2 indicate the same contents. In the figure, 101
, 102 is an amplifier, 111, 112, 113 is a buffer, 121, 122, 123 is an A/D converter, 130 is a video bus, 131 is a CPU, 132 is a digital signal processor (DSP), 133 is a control bus, 134 is a A video bus, 141, 142, and 143 are D/A converters, 151 is a lens system, 152 is a monitor, and 153 is a CRT for recording or original signals.

In this embodiment, one of the broadband amplifiers 101 and 102 for the backscattered electron detection signal is also used for EMF, AEI, and infrared image, and the switch 100
Select the signal to detect. Of course, an amplifier dedicated to each detector may be prepared. The amplified detection signal passes through buffers 111 to 113 and is then sent to an A/D converter 121.
~123, it is converted into a digital signal. The converted digital signal is transmitted through video bus 130 and
It is taken into the PU 131 and DSP 132. CPU13
1 only issues commands without processing image data itself, and monitors and synchronizes the image data transmitted through the video bus 130.
33 to set the processing mode in the DSP 132. Of course, if it is a high-performance CPU131, the CPU
The image data processing unit itself may also perform its own image data processing.

The DSP 132 is a system dedicated to signal processing, and is controlled by the CPU 131 through a control bus 133 to process image data in real time. The processing here includes lens system control data generation processing such as contrast, brightness adjustment, automatic focusing, and astigmatism correction, as well as various image operations such as image inversion, combining multiple signals, addition, subtraction, edge enhancement, and filtering. It is possible to perform processing and add various processing functions by changing the software. The generated control data is then transmitted through the video bus 134 and converted into an analog signal by the D/A converter 141. The D/A converter 141 is connected to the control bus 133, and the settings of the lens system 151 are automatically performed by signals sent from the control bus 133. Further, the calculated image data is transmitted through a video bus, converted into image signals by D/A converters 142 and 143, and displayed on a monitor 152 or on a CRT 153 for recording or displaying original signals.

[0015] In this way, a large amount of image data is transmitted at high speed through the video bus, and by preparing various software, the image is processed in real time by a single DSP, and the processed data is sent to the lens system or display system through the video bus. By transmitting up to 100 kHz, the number of amplification stages can be reduced and band deterioration and S/N ratio deterioration can be prevented.

[0016]

As described above, according to the present invention, image data is digitized and signal processed through a video bus, so if the bandwidth of the input stage and output stage amplifiers for analog signals is secured, for example, 10 MHz. Band deterioration does not occur. In addition, since the amplifier system has only two stages, the input stage and the output stage, it is possible to prevent S/N deterioration, and it is also possible to perform various calculations with one DSP, simplifying the system configuration. can be made into
As a result, it is possible to reduce the occurrence of troubles.

[Brief explanation of drawings]

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

FIG. 2 is a diagram showing a signal processing system of a conventional scanning electron microscope.

[Explanation of symbols]

11... Secondary electron detector, 12... Backscattered electron detector, 13...
EMF detector, 14... AEI detector, 15 is an infrared detector, 101, 102... amplifier, 111, 112, 113
...Buffer, 121, 122, 123...A/D converter,
130...Video bus, 131...CPU, 132...Digital signal processor, 133...Control bus, 134...Video bus, 141, 142, 143...D/A converter, 151...Lens system, 152...Monitor, 153...For recording or CRT for original signal.

Claims (1)

[Claims] Claim 1: In a scanning electron microscope that irradiates a sample with an electron beam, detects sample information using one or more detectors, and processes and displays the detected signal, the detected analog signal is converted into a digital signal. An A/D converter that converts the A/D converter into
A video bus that transmits D-converted image data, a digital signal processing circuit that processes image data input through the video bus, a CPU that controls the digital signal processing circuit through a control bus, and output data of the digital signal processing circuit. 1. A signal processing system for a scanning electron microscope using a video bus, comprising: a video bus for transmitting data; and a D/A converter for converting processed data transmitted through the video bus into analog signals.