JPH0620059B2 - Ion beam processing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ion beam processing method, and more particularly, to processing a plurality of layers including a conductive layer and a non-conductive layer while monitoring the processing depth. The present invention relates to a suitable ion beam processing method.

[Prior Art] FIG. 6 is a schematic configuration diagram of a focused ion beam processing apparatus. In FIG. 6, the ion beam 1 is extracted by applying a high voltage of several kV to several tens of kV between the ion source 14 and the extraction electrode 15. The extracted ion beam 1 is focused by a lens 16, the cross-sectional shape of the beam is corrected by a stigma 19, is deflected by a deflector 20, and is irradiated on a target 21 which is a workpiece placed on a table 22 and sputters the target 21. To process. At this time, the charged particles of the secondary ions 3 and secondary electrons 4 emitted from the target 21 are the secondary ion detector 28 and the secondary electron detector 29, respectively.
Detected in. These devices are housed in a vacuum chamber 32 which is evacuated by a vacuum pump 33 to a degree of vacuum of 10 ⁻⁶ Torr or more. Incidentally, in order to perform fine processing, the whole is installed on a surface plate 30 which is floated by an air servo mount 31.

In the focused ion beam device having such a configuration, a duoplasmatron ion source is usually used as the ion source 14. This is because the beam current is large and the amount of secondary ions emitted from the target is large.
At that time, the constituent atoms of the surface irradiated with the beam can be identified. Therefore, the processing depth can be controlled by monitoring the secondary ions.

The technique for analyzing in the depth direction is described in detail in "Surface Analysis", page 61, published by Kodansha and edited by Someno and Yasumori.

[Problems to be solved by the invention]

When the processing depth is monitored by detecting the secondary ions, the beam diameter of 1 μm or less cannot be obtained because the beam current needs to be increased. For this reason, L that requires a beam diameter of 1 μm or less
A high-brightness ion source such as a liquid metal ion source is used for processing SI and the like. However, in order to narrow the beam finely, the beam current must be made small, and the ion beam device for LSI processing cannot obtain a sufficient amount of secondary ions to identify the composition on each surface being processed, It is difficult to use this as a processing monitor. The secondary electrons 4 emitted from the target 21 are SEM (Scanning Electron Micros
It can be used to observe the target surface in the same way as
This secondary electron current has little change in each layer being processed, and it is impossible to use this as a processing monitor.

Conventional focused ion beam processing equipment is SIMS (Secondar
y Ion micro Spectroscopy) was the purpose of the analysis, and it was not necessary to detect the end point position of processing. Therefore,
No consideration is given to monitoring the machining depth.
However, in recent years, the multilayer wiring technology for semiconductor integrated circuits has advanced, and ion beam processing equipment has come to be used for processing semiconductor integrated circuits. Therefore, in the ion beam processing, a technique capable of accurately monitoring the processing depth has been required.

In order to monitor the processing depth, it is necessary to detect the amount showing a remarkable change in each layer of the LSI to be processed. As the amount, the current that leaks out of the charge of the incident ion beam to the Si substrate and flows out is the most appropriate in consideration of the change of current in each layer and the ease of detection. However, simply detecting the leak current does not work. This is because the change in current is relatively large and effective in the surface layer, but in the lower layer, the influence of the side wall of the processed hole appears and the change in current in each layer becomes unclear.

For example, as shown in FIG. 7, when a workpiece composed of a plurality of SiO ₂ layers and Al layers, which are insulators, is being processed by the ion beam 1, the leakage current flowing out from the Si substrate 11 is When detected by the total 8, the leak current changes as shown in FIG. The symbols A to F in FIG. 7 correspond to A to F on the horizontal axis in FIG. In the experimental example shown in FIG. 8, the changes in the lower layer are relatively clear, and points D and E can be inferred from changes in the leakage current to some extent, but when the workpiece becomes a little more complicated, points D and E It becomes unclear, the processing accuracy is lowered, and the reproducibility is also lowered.

It is an object of the present invention to provide an ion beam processing method capable of monitoring the processing depth with high accuracy and reproducibility.

[Means for solving problems]

The above-mentioned object is to focus an ion beam emitted from an ion source on a workpiece including a plurality of layers of a conductor layer and a non-conductor layer,
In the ion beam processing method of deflecting and irradiating and processing the work piece in the depth direction, the work area of the work piece is processed step by step for each required depth, and processing for each required depth is performed. After that, it is achieved by scanning a local area in the processing area with an ion beam, detecting a current flowing out of the workpiece at the beginning of the scanning, and detecting an end point of the processing from a change in the current.

[Action]

The current flowing out from the workpiece due to the scanning of the ion beam when processing the local region varies depending on whether the processing layer is a conductive layer or a non-conductive layer. For example, when detecting the leak current flowing out from the substrate of the workpiece, the leak current is substantially constant and hardly fluctuates in the local region processing of the non-conductive layer, and the ion current scanning is performed in the local region processing of the conductive layer. The leak current fluctuates. It is possible to know how many conductor layers have been processed depending on how many times the region where the leakage current fluctuates appears during processing in the depth direction of the workpiece. Since the leak current when the local area in the processing area is processed is detected, the adverse effect of the side wall of the processing hole can be avoided.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 3 shows Al layers 34, 35, 36 and Si laminated on the Si substrate 11.
A plurality of O ₂ layers 37, 38, 39 and 40 are shown. In the present embodiment, a case will be described in which the ion beam processing apparatus described in FIG. 6 is used to cut the third Al layer 36.

First, a focused ion beam is first scanned over a wide area of several tens of μm square, and is generated from the surface of the workpiece as a target.
The secondary electrons are detected, and the surface irregularity image is observed to set the region to be processed. Next, match the scanning area to the processing area,
Processing is performed by increasing the ion irradiation density in that region.

For this processing, first, as shown in FIG. 5A, the entire surface of the processing area 5 is scanned n times, for example 25 times. Next, a local region 6 is set in the region other than the region end of the processed region 5 as shown in FIG. 5B, and the local region 6 is scanned once or several times over the entire surface. At this time, the substrate 11 (first
A leak current Is flowing out from a holder (not shown) in which (Fig.) Is installed is measured by an ammeter 8. Incidentally, FIG. 1 shows a state of local area scanning performed when the _second SiO ₂ layer 38 is processed as the processing progresses. When the local area 6 is scanned with an ion beam, the local area 6 is sputtered first. Therefore, after the leak current measurement, in order to eliminate the depression of the local region 6 in the processed region 5, as shown in FIG. 5 (e), the remaining non-local region 12 is subjected to the same number of ion beam scans as the number of local region scans. Scan to process. Then again
The entire surface of the processing region 5 is scanned n times, the ion beam scanning of the local region 6 and the leak current are measured, and the non-local region 12 is processed. By repeating such operations, the workpiece is processed stepwise for each required depth, and the leakage current value based on the ion beam scanning of the local region is measured after the processing of each required depth.

The local area 6 and the processing area 5 are set by controlling the voltage applied to the deflector 20 (FIG. 6). When only the non-local area 12 is processed as shown in FIG. 5 (c), when the ion beam enters the local area 6,
The ion beam is cut off in the middle of the ion beam optical system.

FIG. 2 is a diagram showing a difference in leak current when the processed layer is Al or SiO ₂ . When the local region 6 is continuously processed for 10 minutes, for example, the leak current changes as shown in the graph on the right side of FIG. Although both graphs show similar tendencies as a whole, they are remarkably different between several scans at the start of ion beam irradiation and about 30 seconds after the start of processing in the graph of FIG. That is, when the processed surface is an Al layer, the leak current oscillates in synchronization with beam scanning from the start of irradiation. On the other hand, when the processed surface is the SiO ₂ layer, the leak current is constant and does not change from the start of irradiation to several scans. Therefore, when the workpiece shown in FIG. 3 is processed up to the substrate 11, the leakage current Is obtained by measuring the leakage current Is after stepwise processing for each required depth as shown above is shown in FIG. Like Symbol a in FIG.
~ H corresponds to the depths ah in Fig. 3. Therefore, when the third Al layer 36 is cut and processed, the processing end position can be detected by detecting that there are three peaks where the amplitude of the leakage current becomes large.

The number of scans of the processing area is set based on the required accuracy in the depth direction. For example, beam current 0.7nA, processing area 35μ
In the case of m ² , the average processing speed is 0.09 μm / min. Therefore, if the accuracy of the processing end point is 0.2 μm and the scanning time for one whole surface scanning is 5 sec, 25 times is the number of times of scanning the processing area. In other words, the processing monitor can be performed every 0.2 μm by performing the processing monitor scan once after 25 times of scanning. Further, in the description of the embodiment, the position of the local region is fixed at one position in the central portion of the processing region, but a plurality of positions are set within a range where the end portion of the processing hole in the processing region is not touched, and leakage current is measured every time. When moved to, the processing non-uniformity in the processing area is further reduced.

Furthermore, the leak current described in the embodiment is suitable as the monitor current flowing out from the workpiece, but secondary electrons can also be used. Although an example in which Al is used as the conductor layer and SiO ₂ is used as the non-conductor layer has been described, it goes without saying that the present invention is not limited to these materials.

〔The invention's effect〕

According to the present invention, it is possible to clearly determine whether the processed surface is a conductor layer or a non-conductor layer during processing, so that the processing depth can be accurately controlled. The control accuracy changes depending on the beam current and processing area during processing, but in principle it is also possible to monitor each scan and control with 0.1 μm accuracy.

[Brief description of drawings]

FIG. 1 is a perspective view of a work piece being processed by an ion beam processing method according to an embodiment of the present invention, FIG. 2 is an explanatory view of the principle of the present invention, and FIG. 3 shows a plurality of layers (work piece). FIG. 4 is a vertical structural diagram, FIG. 4 is a graph showing changes in leakage current obtained by the method of one embodiment of the present invention, and FIGS. 5 (a), (b), and (c) are beam scans according to one embodiment of the present invention. Method explanatory drawing, FIG. 6 is a block diagram of the focused ion beam apparatus, FIG. 7 is a cross-sectional view of the LSI being processed, and FIG.
The figure is a graph of changes in leakage current. 1 ... Ion beam, 5 ... Processing area, 6 ... Local area, 8 ... Ammeter, 11 ... Substrate, 12 ... Non-local area, 3
4,35,36 ... Al layer, 37,38,39,40 ... SiO ₂ layer.

Claims (4)

[Claims] 1. A workpiece comprising a plurality of conductive layers and non-conductive layers is focused and deflected by an ion beam emitted from an ion source to irradiate the workpiece in the depth direction. In the ion beam processing method of processing, the processing area of the workpiece is processed step by step at each required depth, and after processing each required depth, the local area in the processing area is scanned with an ion beam. An ion beam processing method characterized in that a current flowing out of a workpiece at the beginning of the scanning is detected, and a processing end point position is detected from a change state of the current. 2. After detecting the current by ion beam scanning to the local region, the same number of ion beam scans as the number of ion beam scans are performed in a non-local region inside the processing region and outside the local region, and thereafter. The ion beam processing method according to claim 1, wherein the processing is performed to the required depth. 3. The ion beam processing method according to claim 1, wherein the local region is moved within the processing region each time the processing of the required depth is performed. 4. The ion beam processing according to claim 1, wherein the current flowing out from the work piece is a leak current flowing out from the substrate of the work piece. Method.