JPH04262354A - Converged ion beam processing device - Google Patents

Abstract

PURPOSE:To make accurate location of the processing position even in case a device involves parts with extremely different secondary electron discharging rate within the observing field of view by providing a means to compress the secondary particle intensity logarithmically for imaging. CONSTITUTION:An ion beam emitted by a liquid metal ion source 100 is converged on a specimen 8 by a condenser lens 101 and an objective lens 107. Secondary electrons generated by the specimen 8 when it is irradiated with this converged ion beam (FIB) are sensed and amplified by a secondary electron sensor 7 and are synchronized with the deflection control to be displayed as a scan ion microscope image (SIM) on CRT 5 of a computer 4. A current signal emitted by the sensor 7 is connected either with a linear amplifier 2 or a logarithmic amplifier 1 through a changeover switch 6. Accordingly a SIM image as logarithmic indication of the secondary electron signal amount is obtained by turning the switch 6, which permits observing the shape of the device over the whole area of the screen. Thus the location of the processing position can be made accurately.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focused ion beam processing apparatus and processing method.

0002

[Prior art] As a conventional technology, Proceedings of International Reliability Physics Symposium, (1989)
Pages 43 to 52 (Proceedings of
International Reliability
y Physics Symposium, (198
9) pp43-52).

0003

[Problems to be Solved by the Invention] The above-mentioned conventional technology uses a focused ion beam to perform device cross-sectional processing and grain observation, and uses a scanning ion microscope image (Scanning Ion Microscope) for processing positioning and observation.
roscope (abbreviated as SIM) is used. SIM
The brightness of the image is modulated by the intensity of secondary electrons, and the relationship between the intensity of secondary electrons and the brightness signal is usually linearly related. This makes it possible to image the shape of the sample accurately and easily.

However, if there are parts of the device with extremely different secondary electron emission rates within the observation field, increasing the sensitivity of the detection system to see the dark parts causes overflow of the bright parts, making it difficult to understand the structure. It's gone. Furthermore, if the sensitivity of the detection system is adjusted to bright areas, structures in dark areas become invisible. Such a situation occurs when there is a conductor pattern at ground potential on the insulating film or when there is an extreme step difference in the device.

An object of the present invention is to enable accurate processing positioning by making it possible to observe the device shape over the entire screen even if there are parts of the device with extremely different secondary electron emission rates within the observation field of view. It's about doing.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a means for logarithmically compressing the secondary particle intensity and converting it into an image was added to the FIB apparatus.

[0007]

[Effect] By logarithmically compressing the secondary particle intensity, the device shape can be observed over the entire screen even if there are parts of the device with extremely different secondary particle emission rates within the observation field. , machining positioning, etc. can be performed accurately.

[0008]

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 is a configuration diagram of the FIB processing apparatus. The ion beam emitted from the liquid metal ion source 100 is focused onto the sample 8 by a condenser lens 101 and an objective lens 107. The beam acceleration voltage is 30 kV. Between the lenses is an aperture 102, an aligner stigma 103,
Blanker 104, blanking aperture 105
, a deflector 106 are arranged. Secondary electrons generated from the sample 8 by FIB irradiation are detected and amplified by the secondary electron detector 7, and displayed as a SIM image on the CRT 5 of the computer 4 by synchronizing with deflection control. The deflection of the beam and the collection of secondary electron signals are supervised by the control device 3. The current signal output from the detector 7 is connected to the linear amplifier 2 or the logarithmic amplifier 1 by a changeover switch 6. Therefore, if switch 6 is turned to the linear amplifier 2 side, the SIM image shows a change in brightness proportional to the amount of secondary electron signal, and if switch 6 is turned to the logarithmic amplifier 1 side, the amount of secondary electron signal is displayed logarithmically. A SIM image is obtained. In addition, the FIB device is connected to a high-voltage power supply, a stage control system, and a vacuum exhaust system.

FIG. 2 shows an example of device cross-section processing using the apparatus of the present invention. The following is a step-by-step explanation. FIG. 2(a) is a SIM image 10 of the surface of the LSI. A contact 12 with the lower layer wiring is formed in the middle of the aluminum wiring 11. A passivation film is formed on the surface of an LSI, and the sensitivity of the secondary electron detector is relatively increased to capture an image. FIG. 2(b) shows how the FIB processing area 13 is specified based on the SIM image. By forming a cross section approximately at the center of the contact 12 and observing it from an oblique direction, it is possible to inspect whether contact with the underlying wiring has been successfully formed. On the premise of observation from an oblique direction, it is necessary to process the square hole to have a relatively large opening (7 μm square in the case of the example). In order to shorten the processing time, the aperture 102 of the FIB device is usually switched to make it larger and the beam current is increased. FIG. 2(c) is a SIM image after high current processing (rough processing: beam current 6 nA). The side walls of the processed hole sag to some extent due to redeposition of sputtered particles from the substrate. Furthermore, the stepped portion has a high secondary electron emission rate, resulting in an image with high contrast. As the next step, in order to obtain a clean cross section, the aperture 102 of the FIB device is changed to be smaller, and the beam is made finer for finishing processing (beam diameter of 0.1 μm or less). First, a SIM image is taken to set the processing area for finishing. S.I.
In the M image, there are a stepped portion 14 and other portions in which the secondary electron emission rate is extremely different. In a normal FIB device, the signal current intensity and the image luminance signal intensity are correlated by a linear function as shown in Figure 4 (however, the signal current intensity is clamped at a certain signal level by the limiter or the maximum output voltage value of the circuit). The secondary electron emission rate of the sample is reflected directly in the image. Therefore, if you lower the gain of the detection system to make it easier to see areas with a high secondary electron emission rate, the shape of the areas with a low secondary electron emission rate will become invisible, and conversely, it will make it easier to see areas with a low secondary electron emission rate. If the gain of the detection system is increased, the portion with a high secondary electron emission rate will become saturated and the shape will no longer be visible. Therefore, the changeover switch 6 is turned to the logarithmic amplifier 1 side, and a logarithmically compressed SIM image is taken. FIG. 2(d) is a logarithmically compressed SIM image, and the shape of the device can be confirmed over the entire screen. FIG. 2(e) shows how the finish processing area 15 is set using a logarithmically compressed SIM image. Compressed images are particularly effective when using computer systems that display fewer gradations on screen. In this example, the logarithmic function shown in FIG. 5(a) was used as the compression function, but signal compression is performed by generating a luminance signal such that the slope (differential value) of the function decreases as the signal current intensity increases. Therefore, the square root function in (b) can also be used (however, the compression effect is different from the logarithm). It is also possible to approximately create the compression function using a broken line.

[0010] In this way, by using the logarithmically compressed SIM image, the processing area could be set accurately. This not only allows you to accurately cut out the desired cross section, but also reduces machining time since no extra areas are included in the finishing area.

FIG. 3 is a circuit diagram of the logarithmic amplifier used in this embodiment. The current ie flowing into the electron multiplier 20 is logarithmically converted into voltage by a logarithmic operational amplifier 21 having a transistor connected to a feedback circuit. In this way, by converting ie into a logarithmically converted voltage signal in the first stage amplifier, a signal with good S/N can be obtained with a simple circuit configuration. The output of the operational amplifier 21 is biased and amplified by a differential amplifier 22 and a bias voltage generation circuit 23, and then output. Transistor characteristics are easily affected by ambient temperature. Therefore, if it is desired to observe the secondary electron signal intensity as an absolute value, it is necessary to add a temperature compensation circuit. However, if you simply want to obtain an image, short-term stability is sufficient for practical use, so a temperature compensation circuit is not necessarily necessary. In addition, AGC (Automatic Control) automatically adjusts the maximum brightness of the image to the set value.
When using a tic gain control circuit, temperature drift can be compensated for by including a logarithmic amplifier in its feedback loop.

In this embodiment, a logarithmic amplifier that utilizes the pn junction characteristics of a transistor is used, but it is also possible to approximate similar signal compression characteristics with a broken line, which makes the circuit more complicated but has characteristics with less temperature drift. can get. Furthermore, if the system is capable of inputting data into a computer at high resolution (multi-bit: for example 16 bits), it is also possible to collect data linearly and compress the data through calculations within the computer.

Although this example relates to cross-sectional processing of a device, it can also be applied to forming a thin wall in a desired part of a device by FIB processing for the purpose of observing a transmission electron microscope image of a specific location on a sample. It is possible.

[0014]

According to the present invention, the shape of the device can be observed over the entire screen even if there are parts of the device with extremely different secondary particle emission rates within the observation field of view. Therefore, there is an effect that positioning for machining can be performed accurately.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a focused ion beam processing apparatus showing an embodiment of the present invention.

FIG. 2 is a diagram showing SIM images of an example of the present invention, and sequentially explains cross-sectional processing of a device.

FIG. 3 is a diagram of a logarithmic amplifier circuit used in an embodiment of the present invention.

FIG. 4 is a graph showing a conventional signal processing function (linear function).

FIG. 5 is a graph showing an example of a signal compression function.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Logarithmic amplifier, 2... Linear amplifier, 3... Deflection/data collection control device, 4... Computer, 5... CRT, 6...
Changeover switch, 7... Secondary electron detector, 8... Sample, 1
0...SIM image, 11...aluminum wiring, 12...contact,
13, 15... Processing area, 14... Step portion, 20... Electron multiplier, 21... Operational amplifier, 22... Differential amplifier, 23... Bias voltage generation circuit, 100... Liquid metal ion source, 10
1...Condenser lens, 102...Aperture, 103
...Aligner Stigma, 104...Blanker, 10
5...Blanking aperture, 106...Deflector, 107...Objective lens, 108...Stage.

Claims (9)

[Claims] Claims 1: A means for accelerating ions and focusing and deflecting them onto a sample; a means for detecting and imaging secondary particles generated from the sample by the ion irradiation; and a means for selectively specifying a specific area based on the image. What is claimed is: 1. A focused ion beam processing device comprising means for irradiating ions onto a target, the focused ion beam processing device having means for imaging secondary particle intensity using a compression function. 2. A circuit for compressing the output signal of the secondary particle detector in an analog manner is used as means for converting the secondary particle intensity into an image using a compression function.
The focused ion beam processing device described. 3. As means for converting the secondary particle intensity into an image using a compression function, the output signal of the secondary particle detector is linearly converted into a digital value, and the converted numerical data is subjected to numerical calculations. 2. The focused ion beam processing apparatus according to claim 1, further comprising a system for compressing and displaying an image. 4. Where the secondary particle intensity is x and the imaging luminance signal intensity is y, the compression function is y=logx, y=xn(
4. The focused ion beam processing apparatus according to claim 1, wherein the focused ion beam processing apparatus is constructed by using a polygonal line approximation of n<1) or a polygonal line approximation thereof. Claim 5: Claim 2 in which the secondary particle detector is of a current output type and uses an amplifier that logarithmically converts the current into a voltage.
The focused ion beam processing device described. 6. The focused ion beam processing apparatus according to claim 3, wherein a circuit for linearly amplifying the output of the secondary particle detector and a circuit for compressing the output of the secondary particle detector are used in combination or in a switching manner. 7. A cross-sectional observation method in which a hole is machined in a sample using the focused ion beam and a cross-section of a side wall of the machined hole is observed from an oblique direction, the method comprising specifying a processing area using the compressed image. 8. A claim characterized in that the hole machining is performed using at least two types of beams having different beam diameters (beam currents), and the compressed image is used during cross-sectional finishing with the fine beams. Section processing method according to item 7. 9. When forming a thin wall on a sample by the focused ion beam processing for the purpose of observing a transmission electron microscope image of a specific location on the sample, the compressed image is used to designate the processing area. Thin wall processing method.